Success! Chemistry - All Questions

INSTRUMENTATION & ANALYTICAL PRINICPLES

Which of the following lamps provides a continuous spectrum of radiant energy in the visible, near IR, and near UV regions of the spectrum?

A. Tungsten-filament

B. Hydrogen

C. Deuterium

D. Mercury vapor

A. Tungsten-filament

A. A tungsten-filament lamp is the most common light source for photometry in the visible region. It provides a continuous spectrum (360-800 nm) from the near infrared (IR) through the visible to the near ultraviolet (UV) region. Most of the radiant energy is in the near IR. Only about 15% is in the visible region—the region usually used. Because of the large emission in the near IR, tungsten lamps generate a significant amount of heat. Hydrogen and deuterium lamps are used for work in the 200-375 nm range. The mercury vapor lamp does not provide a continuous spectrum, emitting radiation at specific wavelengths.

Which of the following isolates light within a narrow region of the spectrum?

A. Photomultiplier tube

B. Monochromator

C. Photovoltaic cell

D. Detector

B. Monochromator

B. Photometric methods are based on the use of Beer's law, which is applicable only for monochromatic light. A monochromator is a device for selecting a narrow band of wavelengths from a continuous spectrum. The three kinds of monochromators are filters, prisms, and diffraction gratings.

Which of the following is not descriptive of a photomultiplier tube?

A. Emits electrons proportionally to initial light absorbed

B. Must be shielded from stray light

C. Cannot be used with a chopper

D. Amplifies the initial signal received

C. Cannot be used with a chopper

C. A photomultiplier tube (PMT) responds to the radiant energy (light) it absorbs by emitting electrons in a proportional amount to the initial light absorbed. These electrons then go through a series of stages where amplification occurs. The cascade effect, as the electrons go through 10 to 15 stages, results in a final current that may be one million times the initial current. The PMT exhibits rapid response time and sensitivity. These qualities also dictate that this type of detector be shielded from stray light and room light to prevent burnout. The rapid response time of a PMT makes it able to monitor interrupted light beams produced by a chopper.

Which of the following is false about a photomultiplier tube?

A. Converts radiant energy (light) to electrical energy (current)

B. Amplifies the current significantly

C. Has a very rapid response time

D. Is composed of an iron plate and a layer of selenium

D. Is composed of an iron plate and a layer of selenium

D. A photomultiplier tube (PMT) has two functions: (1) It is a transducer that converts light to electricity; and (2) it amplifies the signal within the tube. Amplification can be as great as one million times. The emission of electrons by a light-sensitive surface—that is, the conversion of light energy to electrical energy—is virtually instantaneous. Hence, PMTs have a very rapid response time. An iron plate and a layer of selenium are partial descriptions of the composition of a photocell or barrier layer cell.

Which type of photodetector employs a linear arrangement that allows it to respond to a specific wavelength resulting in complete UV/visible spectrum analysis?

A. Photomultiplier tube

B. Phototube

C. Barrier layer cell

D. Photodiode array

D. Photodiode array

D. Photodiode array detectors are designed with 256 to 2048 photodiodes that are arranged in a linear fashion. This arrangement allows each photodiode to respond to a specific wavelength that results in a continuous UV/visible spectrum. Resolution is generally 1-2 nm.

When performing spectrophotometer quality assurance checks, what is the holmium oxide glass filter used to assess?

A. Linearity

B. Stray light

C. Absorbance accuracy

D. Wavelength accuracy

D. Wavelength accuracy

D. Wavelength calibration of a spectrophotometer is performed to verify that the radiant energy emitted from the monochromator

through the exit slit is the same as the wavelength selector indicates. The glass filters holmium oxide, used in the UV and visible ranges, and didymium, used in the visible and near IR regions, are employed to check wavelength accuracy. Solutions of stable chromogens such as nickel sulfate may be used. Source lamps may be replaced with mercury-vapor or deuterium lamps. These lamps have strong emission lines and provide the most accurate method of wavelength calibration.

In spectrophotometric analysis, what is the purpose of the reagent blank?

A. Correct for interfering chromogens

B. Correct for lipemia

C. Correct for protein

D. Correct for color contribution of the reagents

D. Correct for color contribution of the reagents

D. The reagent blank contains the same reagents as those used for assaying the specimen. By adjusting the spectrophotometer to IOQ%T (or 0 absorbance) with the reagent blank, the instrument automatically subtracts the color contributed by the reagents from each succeeding reading of specimens, controls, and standards. This technique is used both in manual procedures and automated instruments. Because the reagent blank does not contain sample, there is no correction for interfering chromogens or lipemia.

In regard to bichromatic analysis, which of the following is false?

A. Absorbance is measured at the spectral absorbance peak for a blank

and the sample using the same wavelength.

B. Eliminates background interferences

C. Sample concentration determined from difference in two measured absorbances

D. Functions as a reference blank for each sample

A. Absorbance is measured at the spectral absorbance peak for a blank

and the sample using the same wavelength.

A. Measurement of an assay at two different wavelengths is termed bichromatic. The wavelengths chosen for absorbance readings will represent the peak and base of the spectral absorbance curve for the particular assay. By determining the difference between the two measured absorbances, the sample's concentration can be calculated with elimination of background interference from such substances as bilirubin and hemoglobin. Thus, bichromatic analysis functions as a reference blank for each individual sample.

The bandpass of a spectrophotometer is 10 nm. If an instalment is set at 540 nm, the wavelengths that are permitted to impinge on the sample will be within what wavelength range?

A. 530-540 nm

B. 530-550 nm

C. 535-545 nm

D. 540-550 nm

C. 535-545 nm

C. The bandpass or bandwidth is the range of wavelengths that are passed by a monochromator. In the example given, the bandpass will permit a 10-nm range of wavelengths to pass through the monochromator and impinge on the sample solution in the cuvet. Thus, 540 ± 5 nm (10-nm bandpass) will be equivalent to a wavelength range of 535-545 nm.

Which of the following formulas is an expression of the Beer-Lambert law that is routinely applied to spectrophotometric analysis?

A. Au X (Cs/As) = Cu

B. Cu X (Cs/As)= Au

C. As X (Cs/Cu) = Au

D. A = 2 - log %T

A. Au X (Cs/As) = Cu

A. When the absorbance of a sample in solution varies directly with the concentration of the sample, Beer's law is followed. In turn, when the absorbance increases exponentially with an increase in the light path, the Lambert law is followed. Incorporation of these two laws may be stated as A = abc, where A = absorbance, a = absorptivity of the substance being measured, b = light path in cm, and c = concentration of the measured substance. When the Beer-Lambert law is applied to spectrophotometric analyses of standards and unknown samples that are being measured, the following equation is derived: &u X CS/AS = Cu, where Au = absorbance of unknown, Cu — concentration of unknown, As = absorbance of standard, and Au = absorbance of unknown. This formula is applied to assays that exhibit linear relationships between changes in absorbance with changes in concentration to calculate the concentration of the unknown sample.

In spectrophotometry, which of the following is a mathematical expression of the relationship between absorbance and transmittance?

A. A = abc

B. Au/Cu = As/Cs

C. A = 2 - log %T

D. A = log %T

C. A = 2 - log %T

C. In spectrophotometry, molecules in solution will cause incident light to be absorbed while the remaining light energy will be transmitted. Absorbance is the term used to describe the monochromatic light that is absorbed by the sample, and transmittance describes the light that passes through the sample. The mathematical relationship between absorbance and transmittance is expressed by A = 2 — log %T.

Which of the following is not a problem inherent in turbidimetry?

A. Variation in particle size of samples

B. Variation in particle size of standards

C. Rate of aggregation or settling of particles

D. Need to maintain a constant and specific temperature

D. Need to maintain a constant and specific temperature

D. Turbidimetry is the measurement of the amount of light blocked by particulate matter in passing through a turbid solution. The amount of light blocked depends on the number and the size of the particles. Hence the particle size in samples and standards must be comparable. Consistent timing of sample preparation and assay helps to avoid errors resulting from aggregation or settling of particles. The procedure is usually carried out at room temperature. Slight variations in temperature are not critical.

Which of the following may be associated with reflectance spectrophotometry as it relates to the dry reagent slide technique?

A. Light projected to the slide at 180-degree angle

B. Dye concentration directly proportional to reflectance

C. Unabsorbed, reflected light detected by photodetector

D. Reflectance values are linearly proportional to transmission values

C. Unabsorbed, reflected light detected by photodetector

C. In the dry reagent slide technique, as light from a radiant energy source passes through an interference filter, it is projected to the slide at a 45-degree angle. The light then follows a path through the clear support material and reagent layer and hits a white spreading layer; the unabsorbed light is then reflected back through the reagent and support layers. This reflected light impinges on the photodetector, which is positioned at a 90-degree angle to the slide. Because reflectance values are neither linearly proportional to transmission values nor consequently to dye concentration, the microcomputer utilizes an algorithm as a linearizing transformation of reflectance values to transmission values so that concentration may be calculated.

Fluorometers are designed so that the path of the exciting light is at a right angle to the path of the emitted light. What is the purpose of this design?

A. Prevent loss of emitted light

B. Prevent loss of the excitation light

C. Focus emitted and excitation light upon the detector

D. Prevent excitation light from reaching the detector

D. Prevent excitation light from reaching the detector

D. In a fluorometer, light from the excitation lamp travels in a straight line, whereas the fluorescent light is radiated in all directions. If the detector for the emitted fluorescent light is placed at a right angle to the path of the excitation light, the excitation light will not fall on the detector. In addition, baffles can be placed around the cuvet to avoid reflection of the exciting light from the surface of the cuvet to the detector. The right-angle configuration does not prevent loss of the exciting or the emitted light.

Which of the following represents a primary advantage of performing fluorometric over absorption spectroscopic methods of analysis?

A. Increased specificity and increased sensitivity

B. Increased specificity and decreased sensitivity

C. Purity of reagents used not as critical

D. Ease of performing assays

A. Increased specificity and increased sensitivity

A. Fluorescence occurs when a molecule absorbs light of a particular wavelength and is thereby stimulated to emit light of a longer wavelength. The emitted light has a characteristic spectrum, the emission spectrum, that is unique for each fluorescing molecule. Hence, fluorometric methods are extremely sensitive and highly specific. Because of this extreme sensitivity, reagents used must be of a higher degree of purity than is required for spectroscopy, because even slight traces of impurities may fluoresce.

Which of the following may be associated with fluorescence polarization?

A. Plane-polarized light is used for sample excitation.

B. Small molecular complexes show a greater amount of polarization.

C. It is a heterogeneous technique employed in fluorophore-ligand immunoassays.

D. Polarized light detected is directly proportional to concentration of ligand in sample.

A. Plane-polarized light is used for sample excitation.

A. Instrumentation employing fluorescence polarization is used for such testing as therapeutic drug levels and fetal lung maturity analysis. In these immunologic assays, plane-polarized light excites fluorophors in the sample cuvet. The free fluorophore-labeled ligands rotate freely because of their small size and primarily emit depolarized light. The labeled ligand-antibody complexes rotate more slowly because of their large size and emit polarized fluorescent light. Because of the differences in emitted light, it is not necessary to separate free from bound fluorophore-labeled ligands, allowing for use of the homogeneous assay technique. The emitted fluorescence intensity is measured by a polarization analyzer in the vertical plane, followed by its 90-degree movement for measurement in the horizontal plane. The amount of polarized light detected is inversely proportional to the concentration of ligand in the serum sample

Which of the following may be associated with bioluminescence?

A. Light emission produced due to enzymatic oxidation of a substrate

B. Less sensitive than direct fluorescent assays

C. Electron excitation caused by radiant energy

D. Employs a radioactive label

A. Light emission produced due to enzymatic oxidation of a substrate

A. Bioluminescence is a type of chemiluminescence in which the excitation energy is supplied by an enzymatic chemical reaction rather than by radiant energy, as in fluorescence and phosphorescence. Bioluminescence assays may employ such systems as NADH:FMN oxidoreductasebacterial luciferase or adenosine triphosphatefirefly luciferase. Bioluminescence assays are nonradioactive, having sensitivity levels in the attomole (1CT18) to zeptomole (10~21) ranges, which makes them more sensitive than direct fluorescence assays. Bioluminescence has been applied in the development of immunoassays

Nephelometry is based on the measurement of light that is

A. Absorbed by particles in suspension

B. Scattered by particles in suspension

C. Produced by fluorescence

D. Produced by excitation of ground-state atoms

B. Scattered by particles in suspension

B. Nephelometry is the measurement of the amount of light scattered by particles in suspension. The amount of light scattered depends on

the size and shape of the particles and on the wavelength of the incident light. Ultraviolet light should not be used because it might produce some fluorescence, which would lead to erroneously high results.

Which of the following instruments is used in the clinical laboratory or in

reference laboratories to detect beta and gamma emissions?

A. Fluorometer

B. Nephelometer

C. Scintillation counter

D. Spectrophotometer

C. Scintillation counter

C. Radionuclides are quantified by measuring the amount of energy that they emit. This can be in the form of alpha emission 2He2+, beta emission (electrons ejected from the nucleus of a radioisotope during radioactive decay), or gamma emission (electromagnetic radiation emitted during radioactive decay). Beta and gamma emissions can be detected by scintillation counters. The sensing element of a scintillation counter is a fluor, a substance capable of converting radiation energy to light energy. The light energy is converted to electrical energy and amplified by a photomultiplier tube. A fluor commonly employed in solid scintillation counters is a large crystal of sodium iodide containing a small amount of thallium as an activator; it is used for gamma counting. Beta emission is counted by liquid scintillation counters using fluors dissolved in organic solvents.

Which of the following best describes chemiluminescence?

A. Electron excitation caused by radiant energy

B. Enzymatic oxidation of a substrate produces light emission

C. Chemical energy excites electrons that emit light upon return to ground state

D. Employs a fluorescent label that produces light

C. Chemical energy excites electrons that emit light upon return to ground state

C. Chemiluminescence is a type of luminescence where excitation does not require absorption of radiant energy. Chemiluminescence is the

process where the chemical energy of a reaction produces excited atoms, and upon electron return to ground state photons of light are emitted. Chemiluminescence has been applied in the development of immunoassays and has ultrasensitivity in the attomole (10~18) to zeptomole (10~21) ranges.

In assaying an analyte with a single-beam atomic absorption spectrophotometer, what is the instrument actually measuring?

A. Intensity of light emitted by the analyte on its return to the ground state

B. Intensity of light that the analyte absorbs from the hollow-cathode lamp

C. Intensity of light that the analyte absorbs from the flame

D. Intensity of the beam from the hollowcathode lamp after it has passed through the analyte-containing flame

D. Intensity of the beam from the hollowcathode lamp after it has passed through the analyte-containing flame

D. Atomic absorption spectrophotometry (AAS) is based on the principle that atoms in a basic ground state are capable of absorbing energy in the form of light at a specific wavelength. In a single-beam AAS, the amount of light that the analyte absorbs from the hollow-cathode lamp is what we wish to know. However, what is actually measured is the intensity of the beam after it has passed through the flame. This measurement is made with and without sample in the flame. In this way, the instrument calculates the amount of

light absorbed because of the presence of the analyte in the flame. Because most samples usually have the analyte in the form of a compound or an ion, the analyte must first be converted to nonionized atoms. This is achieved by heating in a flame. About 99% of the atoms of analyte in the flame are in the ground state and, therefore, are capable of absorbing energy at the appropriate wavelength. Hence, light absorbed is essentially proportional to the concentration of the analyte. The light source in AAS is a hollowcathode lamp in which the cathode contains the element that is to be measured.

What is the function of the flame in atomic absorption spectroscopy?

A. Absorb the energy emitted from the metal analyte in returning to ground state

B. Supply the thermal energy needed to excite the metal analyte

C. Bring the metal analyte to its ground state

D. Supply the light that is absorbed by the metal analyte

C. Bring the metal analyte to its ground state

C. The basis of AAS is the measurement of light, at a specific wavelength, that is absorbed by an element whose atoms are in a ground state. The flame in AAS serves two functions—to accept the sample, thus serving as a cuvet, and to supply heat for converting the element, which is usually present in the sample in molecular form, into its atomic form at ground-state energy level. The hollow-cathode lamp supplies the emission line of light required for the analysis. The metal

element of interest is coated on the cathode of the lamp. When the inert gas, either argon or neon, becomes ionized, it is drawn toward the

cathode. The impact excites the metal element coated on the cathode, resulting in the emission of spectral lines specific for the element. This

light emission is then absorbed by the metal element in the sample. A flameless AAS employs a carbon rod (graphite furnace), tantalum, or platinum to hold the sample in a chamber. The temperature is raised to vaporize the sample being analyzed. The atomized sample then absorbs the light energy from the hollow-cathode lamp. This

technique is more sensitive than the flame method.

Most atomic absorption spectrophotometers incorporate a beam chopper and a tuned amplifier. The purpose of these components is to avoid errors that would be caused by

A. Variations in flame temperature

B. Deterioration of the hollow-cathode lamp

C. Stray light from the hollow-cathode lamp

D. Measurement of light emitted by the analyte

D. Measurement of light emitted by the analyte

D. A beam chopper is a device for interrupting a beam of light so that a pulsed beam is produced. In an atomic absorption spectrophotometer, if the light entering the flame from the hollowcathode lamp is pulsed, then the light leaving the flame will consist of unabsorbed pulsed light

and impulsed light from the flame and from a small amount of emission by excited atoms of the analyte. The detector has an amplifier that is tuned to recognize and amplify only the pulsed signal. Thus errors caused by light from the flame and light emitted by the analyte are avoided. However, the beam chopper and tuned amplifier do not compensate for errors introduced by variations in flame temperature or

In potentiometry, which of the following is considered the standard electrode?

A. Hydrogen electrode

B. Calcium electrode

C. Potassium electrode

D. Copper electrode

A. Hydrogen electrode

A. A half-cell, also called an electrode, is composed of a single metallic conductor surrounded by a solution of electrolyte. An electrochemical cell consists of two half-cells. If two different kinds of half-cells are connected in such a way as to make a complete circuit, a current will flow because of the potential difference between the two electrodes. The connection must be between the two metallic conductors and also between the two electrolyte solutions, usually by means of a salt bridge. In the analytical technique of potentiometry, a comparison is made between the voltage of one half-cell connected to another half-cell. It is customary that all half-cell potentials be compared to the potential generated by a standard electrode. The universally accepted standard half-cell with which all other halfcells are compared is the standard hydrogen electrode, arbitrarily assigned a potential E° of 0.000 volt.

In an electrolytic cell, which of the following is the half-cell where reduction takes place?

A. Anode

B. Cathode

C. Combination electrode

D. Electrode response

B. Cathode

B. Oxidation involves the loss of electrons, and reduction the gain of electrons. In an electrolytic cell composed of two different half-cells—for example, zinc in zinc sulfate and copper in copper sulfate—electrons will flow from the anode to the cathode. Thus reduction takes place at the cathode, whereas oxidation occurs at the anode. "Combination electrode" refers to the combining of indicator and reference electrodes into a single unit. "Electrode response" refers to the ability of an ion-selective electrode to respond to a change in concentration of the ion being measured by exhibiting a change in potential

Mercury covered by a layer of mercurous chloride in contact with saturated potassium chloride solution is a description of which of the following types of electrodes?

A. Sodium

B. Calomel

C. Calcium

D. Silver/silver chloride

B. Calomel

B. In practical applications of potentiometry, it is desirable to use one half-cell with a known and constant potential that is not sensitive to the composition of the material to be analyzed. This is called the reference electrode. One type of reference electrode is the calomel electrode, which consists of mercury covered by a layer of mercurous chloride in contact with a saturated solution of potassium chloride. The other half-cell, called the indicator electrode, is selected on the basis of the change in its potential with change in the concentration of the analyte of interest. The silver-silver chloride electrode is a commonly used type of reference electrode. The sodium and calcium electrodes are types of ionselective electrodes

When a pH-sensitive glass electrode is not actively in use, in what type of solution should it be kept?

A. Tap water

B. Physiologic saline solution

C. The medium recommended by the manufacturer

D. A buffer solution of alkaline pH

C. The medium recommended by the manufacturer

C. For optimum performance, pH-sensitive glass electrodes that are not actively in use should be kept immersed in an aqueous medium. Because the exact composition of the pH-sensitive glass varies from one manufacturer to another, the glass electrode should be maintained in the medium recommended by the manufacturer. Usual media are deionized water, dilute HC1, and buffer with a pH near the pH of the solution to be measured. The functioning of a glass electrode depends on the properties of the pH-sensitive glass. A typical glass electrode is made by sealing a thin piece of pH-sensitive glass at the end of a piece of glass tubing and filling the tube with a solution of hydrochloric acid saturated with silver chloride. A silver wire is immersed in the solution in the tube, with one end extending outside the tube for external connection. This is essentially a silver/silver chloride reference electrode sealed within the tube with the pH-sensitive glass tip. This pH-sensitive glass functions appropriately only when it is saturated with water. Then each surface of the glass develops a hydrated lattice, where exchange of alkaline metal ions in the lattice for hydrogen ions in the test solution can occur.

When measuring K+ with an ion-selective electrode by means of a liquid ionexchange membrane, what antibiotic will be incorporated into the membrane?

A. Monactin

B. Nonactin

C. Streptomycin

D. Valinomycin

D. Valinomycin

D. The ion-exchange electrode is a type of potentiometric, ion-selective electrode that consists of a liquid ion-exchange membrane that is made of an inert solvent and an ion-selective neutral earner material. A collodion membrane may be used to separate the membrane solution from the sample solution being analyzed. Because of its ability to bind K+, the antibiotic valinomycin is used as the neutral carrier for the K+-selective membrane. The antibiotics nonactin and monactin are used in combination as the neutral carrier for the NH^-selective membrane. A special formulation is used to make a selective glass membrane for the measurement of sodium.

Which of the following is false about ion-selective electrode analysis of sodium?

A. Uses a glass membrane

B. Errors occur from protein buildup on the membrane.

C. Membrane coated with valinomycin

D. Principle based on potentiometry

C. Membrane coated with valinomycin

C. Ion-selective electrodes for the measurement of sodium are glass membrane electrodes with selective capability. They are constructed from glass that consists of silicon dioxide, sodium oxide, and aluminum oxide. This type of electrode is based on the principle of potentiometry. Measurement errors may occur from protein buildup on the membrane surface. Potassium is measured using an ion-exchange electrode where the liquid ion-exchange membrane consists of valinomycin as the ionselective carrier.

What are the principles of operation for a chloride analyzer that generates silver ions as part of its reaction mechanism?

A. Potentiometry and amperometry

B. Amperometry and polarography

C. Coulometry and potentiometry

D. Amperometry and coulometry

D. Amperometry and coulometry

D. A chloride coulometer employs a coulometric system based on Faraday's law, which states that in an electrochemical system, the number of equivalent weights of a reactant oxidized or reduced is directly proportional to the quantity of electricity used in the reaction. The quantity of electricity is measured in coulombs. The coulomb is the unit of electrical quantity; 1 coulomb of electricity flowing per minute constitutes a current of 1 ampere. Thus, if the current is constant, the number of equivalent weights of reactant oxidized or reduced depends only on the duration of the current. In the chloride coulometer, the electrochemical reaction is the generation of Ag+ ions by the passage of a direct current across a pair of silver electrodes immersed in a conducting solution containing the sample to be assayed for chloride. As the Ag+ ions are generated, they are immediately removed from solution by combining with chloride to form insoluble silver chloride. When all the chloride is precipitated, further generation of Ag+ ions causes an increase in conductivity of the solution. Thus the instrument provides an electrometric titration, in which the titrant is Ag+ ions and the endpoint of the titration is indicated by the increase in conductivity of the solution. Amperometry is used to measure the increase in conductivity. The amperometric circuit includes a second pair of silver electrodes that are immersed in the solution. They are provided with a small, steady, and constant voltage. The appearance of free Ag+ ions in the solution generates a sharp increase in conductivity, which, in turn, causes a sudden rise in the current between the electrodes in the amperometric circuit. This increase in current activates a relay that stops the further generation of Ag+ ions and also stops an automatic timer placed in the circuit to measure the total duration of current in the coulometric circuit. Although this system is no longer used for routine analysis of serum, it is still employed for sweat chloride analysis.

When quantifying glucose using an amperometric glucose electrode system, which of the following is not a component of the system?

A. Product oxidation produces a current

B. Hydrogen peroxide formed

C. Hexokinase reacts with glucose

D. Platinum electrode

C. Hexokinase reacts with glucose

C. In an amperometric glucose electrode system, glucose oxidase reacts with glucose to produce hydrogen peroxide and gluconic acid. The platinum electrode that operates at a positive potential oxidizes the hydrogen peroxide to oxygen. The oxidation of hydrogen peroxide produces a current that is directly proportional to the glucose level in the sample.

To calibrate the pH electrode in a pH/ blood gas analyzer, it is necessary that

A. The barometric pressure be known and used for adjustments

B. Calibrating gases of known high and low concentrations be used

C. The calibration be performed at room temperature

D. Two buffer solutions of known pH be used

D. Two buffer solutions of known pH be used

D. A pH/blood gas analyzer contains a pHsensitive glass electrode, a PCO^ electrode, and a PO2 electrode. The glass electrode is calibrated by comparison with two primary standard buffers of known pH. Because pH readings are temperature sensitive, the calibration must be carried out at a constant temperature of 37°C. pH readings are not appreciably sensitive to changes in barometric pressure. Note that if the PCO2 and PC>2 electrodes were also to be calibrated, then it would be essential to know the barometric pressure, because that affects the PCC>2 and PO2 calibrating gases.

The measurement of CO2 in blood by means of a PCO2 electrode is dependent on the

A. Passage of H+ ions through the membrane that separates the sample and the electrode

B. Change in pH because of increased carbonic acid in the electrolyte surrounding the electrodes

C. Movement of bicarbonate across the membrane that separates the sample and the electrode

D. Linear relationship between PCO2 in the sample and measured pH

B. Change in pH because of increased carbonic acid in the electrolyte surrounding the electrodes

B. In a blood gas analyzer, the PCO2 electrode is actually a pH electrode immersed in a bicarbonate solution. The bicarbonate solution is separated from the sample by a membrane that is permeable to gaseous CO2 but not to ionized substances such as H+ ions. When CO2 from the sample diffuses across the membrane, it dissolves, forming carbonic acid and thus lowering the pH. The pH is inversely proportional to the log of the PCO2. Hence the scale of the meter can be calibrated directly in terms of PCO2. It should be noted that whereas pH refers to the negative logarithm of the H+ ion concentration, PCO2 refers to the partial pressure of CO2

The measurement of oxygen in blood by means of a PO2 electrode involves which of the following?

A. Wheatstone bridge arrangement of resistive elements sensitive to oxygen concentration

B. Direct relationship between amount of oxygen in the sample and amount of current flowing in the measuring system

C. Change in current resulting from an increase of free silver ions in solution

D. Glass electrode sensitive to H+ ions

B. Direct relationship between amount of oxygen in the sample and amount of current flowing in the measuring system

B. In a blood gas analyzer, the electrode for measuring the partial pressure of oxygen (POz) in the blood is an electrochemical cell consisting of a platinum cathode and a Ag/AgCl anode connected to an external voltage source. The cathode and anode are immersed in buffer. A polypropylene membrane selectively permeable to gases separates the buffer from the blood sample. When there is no oxygen diffusing into the buffer, there is practically no current flowing between the cathode and the anode because they are polarized. When oxygen diffuses into the buffer from a sample, it is reduced at the cathode. The electrons necessary for this reduction are produced at the anode. Hence a current flows; the current is directly proportional to the

PO2 in the sample.

Which of the following blood gas parameters are measured directly by the blood gasanalyzer electrochemically as opposed to being calculated by the instrument?

A. pH, HCO-3, total CO2

B. PCO2, HCO-3, PO2

C. pH, PCO2, PO2

D. PO2, HCO-3, total CO2

C. pH, PCO2, PO2

C. pH, PCO2, and PO2 are measured directly from the specimen by utilizing electrodes. The pH and PCO2 electrodes are potentiometric where the voltage produced across a semipermeable membrane to hydrogen ions or CO2 gas is proportional to the "activity" of those ions in the patient's sample. Activity is measured in voltage whose value can be presented in terms of concentration. PO2 is measured similarly, but using an amperometric electrode. For PO2 a small charge is put on a cathode, and electrons are drawn off the cathode in proportion to the oxygen present. The O2 becomes part of the circuit. The amount of electrons drawn is proportional to the amount of oxygen present. Bicarbonate and other parameters, such as base excess, are calculated by the instrument using pH and PCO2 values and the Henderson/Hasselbalch equation

PROTEINS & TUMOR MARKERS

Proteins, carbohydrates, and lipids are the three major biochemical compounds of human metabolism. What is the element that distinguishes proteins from carbohydrate and lipid compounds?

A. Carbon

B. Hydrogen

C. Oxygen

D. Nitrogen

D. Nitrogen

D. The three major biochemical compounds that exert primary roles in human intermediary metabolism are proteins, carbohydrates, and lipids. The presence of nitrogen in all protein compounds distinguishes proteins from carbohydrates and lipids. Protein compounds contain approximately 16% nitrogen. Although there are only 20 common a-amino acids that are found in all proteins and a total of 40 known amino acids, a protein compound may contain from fifty to thousands of amino acids. The uniqueness of any protein is dictated by the number, type, and

sequencing of the a-amino acids that compose it. The a-amino acids are linked to each other through peptide bonds. A peptide bond is formed through the linkage of the amino group of one amino acid to the carboxyl group of another amino acid.

Proteins may become denatured when subjected to mechanical agitation, heat, or extreme chemical treatment. How are proteins affected by denaturation?

A. Alteration in primary structure

B. Alteration in secondary structure

C. Alteration in tertiary structure

D. Increase in solubility

C. Alteration in tertiary structure

C. A variety of external factors, such as mechanical agitation, application of heat, and extreme chemical treatment with acids or salts, may cause

the denaturation of proteins. When proteins are denatured, they undergo a change in their tertiary structure. Tertiary structure describes the appearance of the protein in its folded, globular form. When the covalent, hydrogen, or disulfide bonds are broken, the protein loses its shape as its polypeptide chain unfolds. With the loss of this tertiary structure, there is also a loss in some of the characteristic properties of the protein. In general, proteins will become less soluble, and enzymes will lose catalytic activity. Denaturation by use of chemicals has been a useful laboratory tool. The mixing of serum proteins with sulfosalicylic acid or trichloroacetic acid causes the precipitation of both the albumin and globulin fractions. When albumin is placed in water, dilute salt solutions, or moderately concentrated salt solutions, it remains soluble. However, the globulins are insoluble in water but soluble in weak salt solutions. Both the albumins and globulins are insoluble in concentrated salt solutions. Primary structure refers to the joining of the amino acids through peptide bonds to form polypeptide chains. Secondary structure refers to the twisting of more than one polypeptide chain into coils or

helices.

What is the basis for the Kjeldahl technique for the determination of serum total protein?

A. Quantification of peptide bonds

B. Determination of the refractive index of proteins

C. Ultraviolet light absorption by aromatic rings at 280 nm

D. Quantification of the nitrogen content of protein

D. Quantification of the nitrogen content of protein

D. Although the Kjeldahl technique for the determination of protein nitrogen is too cumbersome for use in routine testing, it is considered to be the reference method of choice to validate materials used with the biuret method. The Kjeldahl technique is based on the quantification of the nitrogen content of protein. It is estimated that the average nitrogen content of protein is 16% of the total weight. In the Kjeldahl technique, protein undergoes a digestion process with sulfuric acid through which the nitrogen content of the protein is converted to ammonium ion. The ammonium ion in turn may be reacted with Nessler's reagent, forming a colored product that is read spectrophotometrically, or the ammonium ion may undergo distillation, liberating ammonia that is titrated.

When quantifying serum total proteins, upon what is the intensity of the color produced in the biuret reaction dependent?

A. Molecular weight of the protein

B. Acidity of the medium

C. Number of peptide bonds

D. Nitrogen content of the protein

C. Number of peptide bonds

C. A commonly used method to quantify serum total proteins is the biuret procedure. The biuret reaction is based on the complexing of cupric ions in an alkaline solution with the peptide linkages of protein molecules. Because the amino acids of all proteins are joined together by peptide bonds, this method provides an accurate quantification of the total protein content of serum. The greater the amount of protein in a specimen, the greater will be the number of available peptide bonds for reaction and the more intense the colored reaction will be. In the biuret reaction, the intensity of the reddish violet color produced is proportional to the number of peptide bonds present. Generally, one cupric ion complexes with four to six peptide linkages. However, a colored product may be formed when the cupric ion links through coordinate bonds with at least two peptide linkages, with the smallest compound able to react being the tripeptide. Therefore, not only will proteins contribute to the formation of the colored product, but so, too, will any tripeptides and polypeptides present in a serum sample.

Which of the following reagents can be used to measure protein in cerebrospinal fluid?

A. Biuret

B. Coomassie brilliant blue

C. Ponceau S

D. Bromcresol green

B. Coomassie brilliant blue

B. The concentration of total protein in cerebrospinal fluid (CSF) is 15^5 mg/dL. Such a low level of protein requires a method with sufficient sensitivity such as Coomassie brilliant blue. Turbidimetric methods can also be used to quantify protein in CSF. Neither biuret nor Ponceau S has the sensitivity needed, and bromcresol green measures only albumin and does not react with the globulins.

Which disorder is not associated with an elevated protein level in cerebrospinal fluid?

A. Bacterial meningitis

B. Multiple sclerosis

C. Cerebral infarction

D. Hyperthyroidism

D. Hyperthyroidism

D. CSF, an ultrafiltrate of blood plasma, is made in the choroid plexus of the ventricles of the brain. Protein quantification is among the tests generally ordered on CSF; other tests include glucose, culture and sensitivity, and differential cell count. The reference range for CSF protein is 15-45 mg/dL. CSF protein may be quantified using turbidimetric (e.g., sulfosalicylic acid and benzethonium chloride) or dyebinding methods (e.g., Coomassie brilliant blue). Elevated levels of CSF protein are found in such disorders as bacterial, viral, and fungal meningitis; multiple sclerosis; neoplasm; disk herniation; and cerebral infarction. Low levels of CSF protein are found in hyperthyroidism and in CSF leakage from the central nervous system.

Which term describes a congenital disorder that is characterized by a split in the albumin band when serum is subjected to electrophoresis?

A. Analbuminemia

B. Anodic albuminemia

C. Prealbuminemia

D. Bisalbuminemia

D. Bisalbuminemia

D. Bisalbuminemia is a congenital disorder that does not exhibit any clinical manifestations. The only sign of this disorder is the splitting of albumin into two distinct bands when serum is subjected to electrophoresis. The extra albumin band may occur either anodically or cathodically to the normal albumin band depending on its speed of migration. The intensity of the two bands when quantified by densitometry may show that the two forms are of equal concentration. In a less common variation the abnormal albumin band may represent only 10-15% of the total albumin concentration.

In what condition would an increased level of serum albumin be expected?

A. Malnutrition

B. Acute inflammation

C. Dehydration

D. Renal disease

C. Dehydration

C. There are no physiological diseases that cause increased production of albumin by the liver. Elevated serum albumin is only associated with dehydration. It is a relative increase that will return to normal when fluids are administered to alleviate the dehydration. Disorders such as malnutrition, acute inflammation, and renal disease are characterized by decreased serum albumin levels.

Identification of which of the following is useful in early stages of glomerular dysfunction?

A. Microalbuminuria

B. Ketonuria

C. Hematuria

D. Urinary light chains

A. Microalbuminuria

A. In renal disease, glomerular or tubular malfunction results in proteinuria. In early stages of glomerular dysfunction, small quantities of albumin will appear in the urine. Because the concentration is so low, urine dipstick assays are unable to detect the presence of such a small quantity of albumin; hence the term "microalbuminuria." Annual testing of diabetic individuals for microalbuminuria is recommended, because identification of these low levels of albumin that precede nephropathy would allow for clinical intervention to control blood glucose levels and blood pressure. The reference interval for urinary albumin is less than 30 mg/day. Microalbuminuria may be quantified using immunonephelometry and enzyme immunoassay.

Which of the following is a low-weight protein that is found on the cell surfaces of nucleated cells?

A. C-reactive protein

B. beta 2-Microglobulin

C. Ceruloplasmin

D. G^-Macroglobulin

B. beta 2-Microglobulin

B. (32-Microglobulin is a single polypeptide chain that is the light chain component of human leukocyte antigens (HLAs). It is found on the surface of nucleated cells and is notably present on lymphocytes. Increased plasma levels of fi2~ microglobulin are associated with renal failure, lymphocytosis, rheumatoid arthritis, and systemic lupus erythematosus.

Which glycoprotein binds with hemoglobin to facilitate the removal of hemoglobin by the reticuloendothelial system?

A. Haptoglobin

B. Ceruloplasmin

C. cxpAntitrypsin

D. Fibrinogen

A. Haptoglobin

A. Haptoglobin is a glycoprotein produced mainly by the liver that migrates electrophoretically as an alpha2-globulin. Increased serum concentrations of haptoglobin are seen in inflammatory conditions and tissue necrosis, whereas decreased levels are seen in hemolytic situations in which there is extensive red blood cell destruction. In the latter situation, haptoglobin binds with free hemoglobin to form a stable complex that may then be removed by the reticuloendothelial system. Because of the size of the haptoglobin-hemoglobin complex, urinary excretion of hemoglobin by the kidney is avoided, thereby preventing the loss of iron by the kidney.

In a healthy individual, which protein fraction has the greatest concentration in serum?

A. Alphai-globulin

B. Beta-globulin

C. Gamma-globulin

D. Albumin

D. Albumin

D. The serum proteins are divided into five principal fractions based on their electrophoretic mobilities. The five fractions are albumin, alpharglobulin, alpha2-globulin, beta-globulin, and gamma-globulin. Albumin constitutes the largest individual fraction of the serum proteins. The reference concentration of albumin in serum ranges between 3.5 and 5.0 g/dL, and the total globulin concentration is between 2.3 and 3.5 g/dL.

Which of the following is an anionic dye that binds selectively with albumin?

A. Amido black

B. Ponceau S

C. Bromcresol green

D. Coomassie brilliant blue

C. Bromcresol green

C. Bromcresol green (BCG) and bromcresol purple (BCP) are anionic dyes that bind selectively with albumin without preliminary extraction of the globulins. The nature of the dyes is such that the color of the free dye is different from the color of the albumin-dye complex so that the color change is directly proportional to the concentration of albumin in the specimen. Although amido black, Ponceau S, and Coomassie brilliant blue are able to bind albumin, they also react with the globulins, thus prohibiting their use in a direct procedure for quantification of serum albumin.

Which total protein method requires copper sulfate, potassium iodide in

sodium hydroxide, and potassium sodium tartrate in its reagent system?

A. Kjeldahl

B. Biuret

C. Folin-Ciocalteu

D. Ultraviolet absorption

B. Biuret

B. Biuret reagent is a combination of copper sulfate, potassium iodide in sodium hydroxide, and potassium sodium tartrate. The copper sulfate is the key to the reaction because it is the cupric ion that complexes with the peptide bonds of protein. To keep the copper in solution until its use, potassium sodium tartrate is employed as a complexing agent, whereas the autoreduction of copper is prevented by potassium iodide.

Which of the following plasma proteins is not manufactured by the liver?

A. Albumin

B. Haptoglobin

C. Fibrinogen

D. IgG

D. IgG

D. The majority of the plasma proteins are manufactured by the liver. Albumin, fibrinogen, and most of the alpha- and beta-globulins are produced by the liver. The immunoglobulins, including IgG, IgA, IgM, IgD, and IgE, are produced by the lymphoid cells.

There are five immunoglobulin classes:

IgG, IgA, IgM, IgD, and IgE. With which globulin fraction do these immunoglobulins migrate electrophoretically?

A. Alphapglobulins

B. Alpha2-globulins

C. Betapglobulins

D. Gamma-globulins

D. Gamma-globulins

D. The immunoglobulins, IgG, IgA, IgM, IgD, and IgE, migrate electrophoretically with the gamma-globulin fraction. The normal serum levels of the IgD and IgE classes are so low that these two immunoglobulins do not normally contribute to the intensity of the stained gammaglobulin electrophoretic fraction. The primary component of the gamma fraction consists of IgG, with IgA and IgM contributing to the intensity of the stained fraction to a lesser degree. In

disease states the concentration relationship between the immunoglobulins may be significantly altered from the normal.

Of the five immunoglobulin classes, IgG is

the most structurally simple, consisting of

how many light chains/heavy chains,

respectively?

A. 5/2

B. 1/1

C. 2/5

D. 2/2

D. 2/2

D. All the immunoglobulins consist of heavyand light-chain polypeptides. The heavy chains are designated as gamma y, alpha a, mu u, delta A, and epsilon e and are specific for the immunoglobulins IgG, IgA, IgM, IgD, and IgE, respectively. The light chains are designated as kappa K and lambda X, with both types being found in each of the immunoglobulin classes, although the two light chains attached to a particular set of heavy chains must be of the same type. Therefore, IgG consists of two heavy chains of the gamma type and two light chains of either the kappa or lambda type. The immunoglobulins IgA, IgD, and IgE have a structure similar to that of IgG in that they consist of two light chains and two heavy chains of the respective type. IgM is a macromolecule with a pentamer type of structure. IgM consists of five sets of two heavy-chain and two light-chain units, with the basic units being linked to each other by peptide fragments.

Which immunoglobulin class, characterized by its possession of a secretory component, is found in saliva, tears, and body secretions?

A. IgA

B. IgD

C. IgG

D. IgM

A. IgA

A. The immunoglobulin class IgA is found in both plasma and body secretions, with the two types being differentiated by their sedimentation coefficients. Plasma IgA has an average sedimentation coefficient of 7S, and secretory IgA has a sedimentation coefficient of US. Secretory IgA is present in saliva, tears, and secretions of nasal, gastrointestinal, and tracheolbronchial origin. Secretory IgA is dimeric in structure and possesses a glycoprotein secretory component attached to its heavy chains and a J polypeptide. The principal immunoglobulin found in secretions is IgA, with only trace amounts of IgG being present. The presence of IgM, IgD, or IgE in secretions has not been detected.

Which immunoglobulin class is able to cross the placenta from the mother to the fetus?

A. IgA

B. IgD

C. IgE

D. IgG

D. IgG

D. The only immunoglobulin class that is able to cross the placenta from the mother's circulation to the fetus is IgG. Therefore, at birth, there is very little immunoglobulin present in the infant except for the maternal IgG. After birth, as the infant comes in contact with antigens, the levels of IgG, IgA, and IgM slowly increase.

Which of the following is an acute-phase reactant protein able to inhibit enzymatic proteolysis and having the highest concentration of any of the plasma proteolytic inhibitors?

A. C-reactive protein

B. Haptoglobin

C. a2-Macroglobulin

D. a1-Antitrypsin

D. a1-Antitrypsin

D. a1-Antitrypsin is an acute-phase reactant protein whose concentration increases in response to inflammation. a1-Antitrypsin inhibits the selfdestruction of one's own tissue by forming inactive complexes with proteolytic enzymes. In this way the enzymes are inhibited, and tissue

destruction through self-digestion is avoided. a1-Antitrypsin has been found to have the highest concentration in serum of any of the plasma proteolytic inhibitors. It is an effective inhibitor of the enzymes chymotrypsin, plasmin, thrombin, collagenase, and elastase. The primary effect of a1-antitrypsin may be seen in the respiratory tract and the closed spaces of the body where physiological pH values are maintained. a1-Antitrypsin is least effective in the stomach and intestines.

Which of the following is a copper transport protein that migrates as an

alpha2-globulin?

A. Ceruloplasmin

B. Haptoglobin

C. Transferrin

D. Fibrinogen

A. Ceruloplasmin

A. Ceailoplasmin, a metalloprotein, is the principal transport protein of copper in the plasma. In the plasma, copper is primarily bound to

ceruloplasmin, with only very small amounts of copper bound to albumin or in a dialyzable free state. When subjected to an electric field, ceruloplasmin migrates as an alpha2-globulin.

Which of the following proteins is normally produced by the fetus but is

found in increased amounts in the amniotic fluid in cases of spina bifida?

A. a1-Antitrypsin

B. a1-Acid glycoprotein

C. a1-Fetoprotein

D. a2-Macroglobulin

C. a1-Fetoprotein

C. The liver of a fetus and the yolk sac produce a protein known as a1-fetoprotein (AFP). The concentration of AFP in the blood of a fetus

reaches a maximum concentration at approximately 16 to 18 weeks gestation. Blood levels decline from this point and finally disappear

approximately 5 weeks after birth. In cases of open spina bifida or anencephaly, the fetus leaks large amounts of AFP into the amniotic fluid. By means of an amniocentesis, the amount of AFP present in the amniotic fluid may be quantified by enzyme-labeled immunoassay and other immunoassay techniques.

The physician is concerned that a pregnant patient may be at risk for delivering prematurely. What would be the best biochemical marker to measure to assess the situation?

A. Inhibin A

B. a1-Fetoprotein

C. Fetal fibronectin

D. Human chorionic gonadotropin

C. Fetal fibronectin

C. Fibronectin is an adhesive glycoprotein that functions with collagen to support cell adhesion. It is a normal constituent in the placenta and amniotic fluid. As labor begins, a change occurs in cell adhesion that affects the placenta and uterine wall. The level of fetal fibronectin increases in the secretions of the cervix and vagina. When this occurs prematurely, the increase in fetal fibronectin is used to predict risk of premature birth. Inhibin A, ctrfetoprotein, human chorionic gonadotropin, and unconjugated estriol are used together in the quadruple test to assess risk for such disorders as Down syndrome

Bence Jones proteinuria is a condition characterized by the urinary excretion of what type of light chain?

A. Kappa light chains

B. Lambda light chains

C. Both kappa and lambda light chains

D. Either kappa or lambda light chains

D. Either kappa or lambda light chains

D. The immunoglobulins are composed of both heavy and light chains. In Bence Jones proteinuria, there is an overproduction of one type of light

chain by a single clone of plasma cells. Therefore, the plasma cells produce either an excessive amount of kappa light chains or an excessive amount of lambda light chains. The light-chain type produced is in such abundance that the renal threshold is exceeded, resulting in the excretion of free light chains of the kappa or lambda type in the urine. The type of light chain excreted in the urine may be identified by performing immunoelectrophoresis on a concentrated urine specimen. In addition, immunoturbidimetric and immunonephelometric methods may also be used.

Which of the following is not characteristic of multiple myeloma?

A. Monoclonal band in the gamma region

B. Hypercalcemia

C. Hyperalbuminemia

D. Hyperglobulinemia

C. Hyperalbuminemia

C. In multiple myeloma there is an abnormal proliferation of plasma cells. These plasma cells produce a homogeneous immunoglobulin protein that stains as a well-defined peak in the gamma region. Because of the presence of this monoclonal protein, the serum total protein will be elevated. Bone destruction is commonly seen in this disorder, with the plasma cells forming densely packed groups in the lytic areas. Hypercalcemia is primarily the result of bone destruction.

What technique is used to quantify specific immunoglobulin classes?

A. Immunonephelometry

B. Serum protein electrophoresis

C. Isoelectric focusing

D. Immunoelectrophoresis

A. Immunonephelometry

A. Immunonephelometric and immunoturbidimetric techniques are used to quantify specific immunoglobulin classes. Nephelometric techniques used to quantify the immunoglobulins are based on the measurement of light scatter by the antigen-antibody complexes formed. This method also calls for the comparison of unknowns with standards. Although radial immunodiffusion can be used to quantify the immunoglobulins, it is not a method of choice. Serum protein electrophoresis, immunoelectrophoresis, and isoelectric focusing cannot be used to quantify the immunoglobulins

Portal cirrhosis is a chronic disease of the liver. As observed on an electrophoretic serum protein pattern, what is a predominant characteristic of this disease?

A. Monoclonal band in the gammaglobulin region

B. Polyclonal band in the gammaglobulin region

C. Bridging effect between the beta- and gamma-globulin bands

D. Increase in the alpha2-globulin band

C. Bridging effect between the beta- and gamma-globulin bands

C. Portal cirrhosis is a chronic disease of the liver in which fibrosis occurs as a result of tissue necrosis and diffuse small nodules form as liver cells regenerate, with a concomitant distortion of liver structure. The cause of this disorder may include alcoholism, malnutrition, or submassive hepatic necrosis. When a serum protein electrophoresis is performed, the characteristic pattern seen in portal cirrhosis is an elevation of both the gamma- and beta-globulin regions, with these two regions showing a bridging or fusing appearance. This beta-gamma bridging effect is due to an increased level of IgA, which migrates with beta mobility. It should also be noted that the albumin level is depressed.

The abnormal metabolism of several of the amino acids has been linked with disorders classified as inborn errors of metabolism. What technique is used to differentiate among several different amino acids?

A. Electrophoresis

B. Microbiological analysis

C. Enzyme immunoassay

D. Chromatography

D. Chromatography

D. Although microbiological analysis and chemical analysis may be employed to detect and quantify a specific amino acid, chromatographic analysis is preferred as a screening technique for amino acid abnormalities or when differentiation among several amino acids is

necessary. Thin-layer chromatography, either one- or two-dimensional, is being used in conjunction with a mixture of ninhydrin-collidine for color development. To quantify amino acids high-performance liquid chromatography, ion-exchange chromatography, and tandem mass spectrometry are used.

Serum protein electrophoresis is routinely performed on the serum obtained from a clotted blood specimen. If a plasma specimen is substituted for serum, how will the electrophoresis be affected?

A. Electrophoresis cannot be performed because the anticoagulant will

retard the mobilities of the protein fractions.

B. Electrophoresis cannot be performed because the anticoagulant will cause migration of the protein fractions in the direction of the cathode.

C. Electrophoresis will show an extra fraction in the beta-gamma

region.

D. Electrophoresis will show an extra fraction in the prealbumin area.

C. Electrophoresis will show an extra fraction in the beta-gamma

region.

C. Protein electrophoresis is performed on a serum specimen. If plasma is substituted for serum, the electrophoresis will show an extra fraction in the beta-gamma region, because fibrinogen is a beta2-globulin. This extra fraction represents the protein fibrinogen that is present in a plasma specimen. Fibrinogen contributes approximately 0.2-0.4 g/dL to the total protein concentration.

In serum protein electrophoresis, when a barbital buffer of pH 8.6 is employed, what protein fraction will migrate the fastest toward the anode?

A. Albumin

B. Alpha!-globulin

C. Beta-globulin

D. Gamma-globulin

A. Albumin

A. When serum proteins are exposed to a buffer solution of pH 8.6, the proteins take on a net negative charge. The negatively charged proteins will migrate toward the anode (+) when exposed to an electrical field. Albumin migrates the fastest toward the anode whereas the gamma globulins remain close to the point of application and actually move slightly in a cathodic (-) direction because of the effects of endosmosis. The order of migration of the serum proteins, starting at the anode with the fastest-moving fraction, is albumin, alpha)-globulin, alpha2- globulin, beta-globulin, and gamma-globulin.

In which of the following disorders would the maternal serum level of aj-fetoprotein not be elevated?

A. Neural tube defect

B. Spinabifida

C. Fetal distress

D. Down syndrome

D. Down syndrome

D. ctpFetoprotein, synthesized by the fetus, peaks at 13 weeks and declines at 34 weeks of gestation. When concern exists for the wellbeing of the fetus, maternal serum AFP is measured between 15 and 20 weeks of gestation. An increased AFP level in maternal serum is associated with such disorders as neural tube defects, spina bifida, and fetal distress. A decreased AFP level in maternal serum is characteristic of Down syndrome.

A male patient, 48 years old, mentions during his annual physical that he has been having difficulty urinating. The physician performs a rectal examination, and he orders a total prostate-specific antigen (PSA) and free PSA. The patient has the tests done the following week, and the total PSA result is 3.1 ng/mL and the free PSA is 0.3 ng/mL. What do these

results suggest?

A. Both are normal, no disease present

B. Benign prostatic hypertrophy

C. Increased risk of prostate cancer

D. Free PSA is low and does not correlate with total PSA

C. Increased risk of prostate cancer

C. The normal range for total PSA is sometimes referenced as less than 4.0 ng/mL. Early detection guidelines endorse a lower cutoff for total PSA up to 2.5 ng/mL and recommend that values >2.5 ng/mL should be followed up by performing a biopsy. Men with prostate cancer tend to have lower % free PSA (free PSA/total PSA) than men with benign disease; thus lower % free PSA is associated with a higher risk of prostate cancer. In the case presented, the patient's total PSA was 3.1 ng/mL with a free PSA of 0.3 ng/mL, which is 10% free PSA. This low percentage is suggestive of a higher probability of cancer, whereas a percentage >25% is associated with lower risk of cancer.

Which of the following is not associated with carcinoembryonic antigen?

A. Increased levels seen with malignancies of the lungs

B. Quantified by using capillary electrophoresis

C. Used to monitor treatment of colon cancer

D. Glycoprotein in nature

B. Quantified by using capillary electrophoresis

B. Carcinoembryonic antigen (CEA), a glycoprotein, is found in increased amounts in serum when malignant tumors of the colon, lung, pancreas, stomach, and breast are present. Care must be exercised in treating CEA as a diagnostic test, because elevated values are also seen in smokers, hepatitis patients, and patients with several other nonmalignant disorders. Clinically, CEA is more valuable in prognosis and treatment monitoring. Enzyme immunoassay and other types of immunoassays are available for the quantification of CEA.

In cases of hepatoma, which protein not normally found in adult serum is synthesized by liver cells?

A. a1-Acid glycoprotein

B. a1-Fetoprotein

C. a2-Macroglobulin

D. Carcinoembryonic antigen

B. a1-Fetoprotein

B. AFP is normally produced only by the fetus, with blood levels disappearing shortly after birth. However, in the adult, such conditions as

hepatoma or teratoma stimulate the production of this primitive protein by the tumor cells. The quantification of AFP may be used both diagnostically and as a monitor of chemotherapy.

Which of the following is false about PSA?

A. Serum quantified using immunoassays

B. Single-chain glycoprotein

C. Used as a tumor marker

D. Not elevated in benign prostatic hyperplasia

D. Not elevated in benign prostatic hyperplasia

D. PSA is a single-chain glycoprotein whose function aids in the liquefaction of seminal coagulum. PSA is found specifically in the prostate gland, and elevated levels are associated with prostate cancer and benign prostatic hyperplasia (BPH). Thus, combining the quantification of PSA with the performance of the digital rectal examination is more beneficial for prostate cancer detection. Immunoassays using enzyme, fluorescent, and chemiluminescent labels are available to quantify PSA.

Which of the following is an oncofetal antigen that is elevated in nonmucinous epithelial ovarian cancer?

A. CA549

B. CA 125

C. CA 19-9

D. CA 15-3

B. CA 125

B. CA 125 is an oncofetal antigen, glycoprotein in nature, that is produced by ovarian epithelial cells. The majority of individuals with nonmucinous epithelial ovarian cancer exhibit elevated levels of CA 125. CA 125 is also increased in other malignancies, including endometrial, breast, colon, pancreas, and lung cancers. Several benign disorders also exhibit CA 125 elevated levels. It appears that the primary usefulness of CA 125 is in monitoring the success of therapy in treating ovarian carcinoma.

Which of the following is a sialylated Lewis blood group antigen associated with colorectal carcinoma?

A. CA 19-9

B. CA 15-3

C. CA549

D. CEA

A. CA 19-9

A. CA 19-9 is an oncofetal protein that is a sialylated Lewis blood group antigen. It is found in increased levels in colorectal carcinoma as well as in gastric, hepatobiliary, and pancreatic cancers. CA 19-9 is also elevated in several benign disorders, including pancreatitis, extra-hepatic cholestasis, and cirrhosis. The combination use of CA 19-9 and CEA (carcinoembryonic antigen) is helpful in monitoring the recurrence of colorectal cancer.

Which of the following disorders is not associated with an elevation of serum a1-fetoprotein?

A. Testicular germ cell tumors

B. Prostatic carcinoma

C. Pancreatic carcinoma

D. Gastric carcinoma

B. Prostatic carcinoma

B. Elevations of serum levels of AFP are found in a number of malignant as well as benign disorders. Although AFP is considered the most specific laboratory test for hepatocellular carcinoma, increased levels are also found in benign liver disease, including viral hepatitis, chronic active hepatitis, and cirrhosis. Other malignant disorders associated with increased levels of AFP include testicular and ovarian germ cell tumors, pancreatic carcinoma, gastric carcinoma, and colonic carcinoma. Thus, AFP is not a tissue-specific tumor marker AFP is not elevated in prostatic cancer, which is characterized by an elevation in PSA. The use of AFP in conjunction with human chorionic gonadotropin (hCG) is effective in monitoring treatment and identifying recurrence of testicular cancer.

Which of the following is not associated with human chorionic gonadotropin?

A. beta subunit confers immunogenic specificity

B. Used to confirm pregnancy

C. Used as a tumor marker

D. Found in hepatoma

D. Found in hepatoma

D. hCG is a dimer consisting of alpha and beta polypeptide chains, with the beta subunit conferring immunogenic specificity. Although hCG is more commonly associated with testing to confirm pregnancy, it is also associated with certain forms of cancer. beta-hCG is used as a tumor marker for hydatidiform mole, gestational choriocarcinoma, and placental-site trophoblastic tumor. hCG's utility also extends to monitoring the success of therapy in testicular and ovarian germ cell tumors. In addition, increased levels of hCG have been identified in hematopoietic malignancy, melanoma, gastrointestinal tract neoplasms, sarcoma, and lung, breast, and renal cancers.

Although serum elevations are not generally seen in early stages, which of the following tumor markers are elevated in more advanced stages of breast cancer?

A. CEA and AFP

B. AFP and C A 125

C. PSA and CA 15-3

D. CA 15-3 and CA 549

D. CA 15-3 and CA 549

D. CA 15-3 and CA 549 are oncofetal antigens that are glycoprotein in nature. CA 15-3 is found on mammary epithelium. Increased serum levels of CA 15-3 are found in breast, pancreatic, lung, colorectal, and liver cancers. CA 549 is found in the cell membrane and luminal surface of breast tissue. Increased serum levels of CA 549 are found in breast, lung, prostate, and colon cancers. Although both CA 15-3 and CA 549 are elevated in more advanced stages of breast cancer, neither is helpful in detecting early stages of breast cancer.

NONPROTEIN NITROGENOUS COMPOUNDS

What is the compound that comprises the majority of the nonprotein-nitrogen fractions in serum?

A. Uric acid

B. Creatinine

C. Ammonia

D. Urea

D. Urea

D. Constituents in the plasma that contain the element nitrogen are categorized as being protein- or nonprotein-nitrogen compounds. The principal substances included among the nonprotein-nitrogen compounds are urea, amino acids, uric acid, creatinine, creatine, and ammonia. Of these compounds, urea is present in the plasma in the greatest concentration, comprising approximately 45% of the nonprotein-nitrogen fraction.

Express 30 mg/dL of urea nitrogen as urea.

A. 14 mg/dL

B. 20 mg/dL

C. 50 mg/dL

D. 64 mg/dL

D. 64 mg/dL

D. Because the substances classified as nonprotein-nitrogen (NPN) compounds were quantified by assaying for their nitrogen content, it became customary to express urea as urea nitrogen. When urea was expressed as urea nitrogen, a comparison could be made between the concentration of urea and the concentration of other NPN compounds. When it is necessary to convert urea nitrogen values to urea, the concentration may be calculated easily by multiplying the urea nitrogen value by 2.14. This factor is derived from the molecular mass of urea (60 daltons) and the molecular weight of its two nitrogen atoms (28):

60/28= 2.14

In the urea method, the enzymatic action of urease is inhibited when blood for analysis is drawn in a tube containing what anticoagulant?

A. Sodium heparin

B. Sodium fluoride

C. Sodium oxalate

D. Ethylenediaminetetra-acetic acid

B. Sodium fluoride

B. In addition to the fact that sodium fluoride is a weak anticoagulant, it also functions as an antiglycolytic agent and is used as a preservative for glucose in blood specimens. With the urease reagent systems for the quantification of urea, the use of sodium fluoride must be avoided because of its inhibitory effect on this system. Additionally, contamination from the use of ammonium oxalate and ammonium heparin must be avoided, because urease catalyzes the production of ammonium carbonate from urea. In several methods, the ammonium ion formed reacts proportionally to the amount of urea originally present in the sample. Anticoagulants containing ammonium would contribute falsely to the urea result.

In the diacetyl method, what does diacetyl react with to form a yellow product?

A. Ammonia

B. Urea

C. Uric acid

D. Nitrogen

B. Urea

B. In the diacetyl method, acidic diacetyl reacts directly with urea to form a yellow-diazine derivative. Thiosemicarbazide and ferric ions are reagents used to intensify the color of the reaction. Because urea is quantified directly, the method does not suffer from interferences from ammonia contamination, as do some of the urea methods.

What endogenous substance may cause a positive interference in the urease/glutamate dehydrogenase assay?

A. Ammonia

B. Creatinine

C. Glucose

D. Cholesterol

A. Ammonia

A. Adequate specificity is generally obtained when using the urease/glutamate dehydrogenase method. Because urease hydrolyzes urea to ammonia and water, a positive interference from endogenous ammonia will occur with elevated blood levels of ammonia. Such interference may occur from use of aged blood specimens and in certain metabolic diseases.

Which of the following methods utilizes urease and glutamate dehydrogenase for the quantification of serum urea?

A. Berthelot

B. Coupled enzymatic

C. Conductimetric

D. Indicator dye

B. Coupled enzymatic

B. An enzymatic method for quantifying urea employs urease and glutamate dehydrogenase (GLDH) in a coupled enzymatic reaction. Urease catalyzes the production of ammonium carbonate from urea. The ammonium ion produced reacts with 2-oxoglutarate and NADH in the presence of GLDH with the formation of NAD+ and glutamate. The decrease in absorbance, as NADH is oxidized to NAD+, is followed kinetically at 340 nm using a spectrophotometer. In the conductimetric method, the formation of ammonium ions and carbonate ions, from the ammonium carbonate, causes a change in conductivity that is related to the amount of urea present in the sample.

In the Berthelot reaction, what contaminant will cause the urea level to be falsely elevated?

A. Sodium fluoride

B. Protein

C. Ammonia

D. Bacteria

C. Ammonia

C. The Berthelot reaction is based on the production of a blue indophenol compound when ammonia reacts in an alkaline medium with phenol and sodium hypochlorite. This basic colorimetric reaction can be used to quantify both urea and blood ammonia levels. Therefore, any ammonia contamination (i.e., in the distilled water used to make reagents for the urea procedure and on glassware) must be avoided so that falsely elevated urea values will not be obtained.

To maintain acid-base balance, it is necessary that the blood ammonia level be kept within narrow limits. This is accomplished primarily by which of the following?

A. Synthesis of urea from ammonia

B. Synthesis of glutamine from ammonia

C. Excretion of ammonia in the bile

D. Excretion of ammonia in the stools

A. Synthesis of urea from ammonia

A. The catabolism of some amino acids involves a transamination reaction in which the a-amino group of the amino acid is enzymatically removed. After its removal, the a-amino group is transferred to an a-keto acid (a-ketoglutarate) with the formation of L-glutamate. Glutamate, which is the common product formed by most transaminase reactions, then may undergo oxidative deamination in the liver mitochondria with the formation of ammonia. The ammonia thus formed leaves the mitochondria as the amino group of citrulline. Citrulline, in turn, condenses with aspartate, which contains the second amino group needed for urea synthesis, forming argininosuccinate, which ultimately leads to the formation of urea. Therefore, the formation of urea and its excretion in the urine provide the principal means by which the body is able to free itself of excess ammonia.

When a blood ammonia determination is performed, the blood specimen must be treated in a manner that will ensure that

A. The deamination process continues in vitro

B. Glutamine formation in vitro is avoided

C. The transamination process continues in vitro

D. Ammonia formation in vitro is avoided

D. Ammonia formation in vitro is avoided

D. It is necessary that certain precautions in specimen handling be exercised because the enzymatic process of deamination of amides continues at room temperature after a blood sample is drawn. When blood is drawn for ammonia analysis, it is critical that any in vitro ammonia formation be prevented. It is recommended that the tube containing the blood specimen be placed in an ice bath immediately after the blood is drawn, because the cold environment will help retard metabolic processes. It is also important that the chemical analysis of the specimen be started within 20 minutes of drawing the specimen.

Which of the following does not need to be done when collecting, handling, and using a specimen for ammonia analysis?

A. Avoid using a hemolyzed specimen.

B. Collect blood in EDTA or heparin evacuated tubes.

C. Place specimen in a 37°C water bath immediately.

D. Advise patient not to smoke for 8 hours before blood collection.

C. Place specimen in a 37°C water bath immediately.

C. Plasma is the specimen of choice for ammonia analysis. Ethylenediaminetetra-acetic acid (EDTA) and heparin (not the ammonium salt) are acceptable anticoagulants. Because exposure of blood to air is contraindicated, the evacuated blood collection tube should be filled completely. The blood specimen should be placed on ice immediately and centrifuged as soon as possible to inhibit deamination of amino acids. Because the concentration of ammonia in red blood cells is approximately three times greater than in plasma, the analysis should be performed on a nonhemolyzed specimen. Because of the false increase in ammonia levels caused by smoking, patients should be instructed to refrain from smoking for 8 hours before blood collection.

Which of the following statements can be associated with the enzymatic assay of ammonia?

A. Increase in absorbance monitored at 340 nm

B. Nicotinamide-adenine dinucleotide (NAD+) required as a cofactor

C. Ammonium ion isolated from specimen before the enzymatic step

D. Reaction catalyzed by glutamate dehydrogenase

D. Reaction catalyzed by glutamate dehydrogenase

D. Ion-exchange, ion-selective electrode, and enzymatic methods have been employed for the analysis of ammonia in plasma specimens. Because the enzymatic method is a direct assay, prior separation of ammonium ions is not required. The enzymatic reaction catalyzed by glutamate dehydrogenase follows:

2-Oxoglutarate + NHj + NADPH <-->Glutamate + NADP+ + H2O

The rate of oxidation of NADPH to NADP+ is followed as a decreasing change in absorbance at 340 nm.

Which of the following disorders is not associated with an elevated blood ammonia level?

A. Reye syndrome

B. Renal failure

C. Chronic liver failure

D. Diabetes mellitus

D. Diabetes mellitus

D. The gastrointestinal tract is the primary source of blood ammonia. With normal liver function, ammonia is metabolized to urea for urinary excretion. When blood ammonia levels become elevated, toxicity of the central nervous system occurs. Diseases associated with elevated blood ammonia levels include Reye syndrome, renal failure, chronic liver failure, cirrhosis, and hepatic encephalopathy.

An increased serum level of which of the following analytes is most commonly associated with decreased glomerular filtration?

A. Creatinine

B. Uric acid

C. Urea

D. Ammonia

A. Creatinine

A. Creatinine is a waste product of muscle metabolism and as such its production is rather constant on a daily basis. Creatinine is freely filtered by the glomerulus, with only a very small amount secreted by the proximal tubule. Thus, measurement of creatinine is a reflection of glomerular filtration. An increase in the serum creatinine level would be indicative of decreased glomerular filtration. Although uric acid, urea, and ammonia levels may be increased with decreased glomerular filtration, increased levels of these analytes are associated with a number of specific metabolic diseases and, therefore, they are not used as indicators of the glomerular filtration rate.

A serum creatinine was found to be 6.0 mg/dL. Which of the following urea nitrogen serum results would support the same pathological condition?

A. 6 mg/dL

B. 20 mg/dL

C. 35 mg/dL

D. 70 mg/dL

D. 70 mg/dL

D. Serum urea nitrogen and creatinine levels are frequently requested together so that their ratio can be evaluated. The normal ratio of serum urea nitrogen to creatinine ranges between 10:1 and 20:1. Abnormal values obtained when kidney function tests are performed may be the result of a prerenal, renal, or postrenal malfunction. The ratio of urea nitrogen to creatinine is sometimes used as an index in the assessment of kidney function and as a means of differentiating the source of the malfunction.

From what precursor is creatinine formed?

A. Urea

B. Glucose

C. Creatine

D. Uric acid

C. Creatine

C. Creatine is synthesized from the amino acids arginine, glycine, and methionine. In tissues that include the kidneys, small intestinal mucosa,

pancreas, and liver, arginine and glycine form guanidoacetate through a transaminidase reaction. The guanidoacetate is transported in the blood to the liver, where it reacts with S-adenosylmethionine through a transmethylase reaction to form creatine. Creatine is transported in the blood to muscle tissue. Creatine in the form of phosphocreatine is a high-energy storage compound that provides the phosphate needed to produce adenosine triphosphate (ATP) for muscle metabolism. When ATP is formed from phosphocreatine, free creatine is also released. Creatine, through a spontaneous and irreversible reaction, forms creatinine. Creatinine serves no functional metabolic role. It is excreted in the urine as a waste product of creatine.

What analyte is measured using the Jaffe reaction?

A. Urea

B. Uric acid

C. Ammonia

D. Creatinine

D. Creatinine

D. The Jaffe reaction, which was described in 1886, is still used for creatinine analysis. The Jaffe reaction employs the use of an alkaline picrate solution that reacts with creatinine to form a bright

orange-red complex. A drawback to this procedure is its lack of specificity for creatinine, because noncreatinine chromogens, glucose, and proteins are also able to react with alkaline picrate.

When the Jaffe reaction is employed as a kinetic assay to quantify serum creatinine, which of the following is used in the analysis?

A. Serum sample used directly

B. Folin-Wu filtrate

C. Somogyi-Nelson filtrate

D. Trichloroacetic acid filtrate

A. Serum sample used directly

A. Because protein will interfere with the Jaffe reaction, serum for a manual creatinine analysis is treated with sodium tungstate and sulfuric acid to precipitate the proteins. The use of tungstic acid to make a protein-free filtrate is known as the FolinWu method. The protein-free filtrate, which still contains creatinine and other reducing substances, is then mixed with alkaline picrate reagent to yield the characteristic Jaffe reaction. Automated methods have replaced manual methods. These kinetic methods using the alkaline picrate reagent system have been adapted to use small volumes of serum and have readings taken within a short interval of 25-60 sec following initiation of the reaction. Because of the speed at which the analysis is performed and the small serum sample requirement, serum may be used directly, alleviating the need for a protein-free filtrate.

The creatinine clearance test is routinely used to assess the glomerular filtration rate. Given the following information for an average-size adult, calculate a creatinine clearance.

Urine creatinine—120 mg/dL

Plasma creatinine—1.2 mg/dL

Urine volume for 24 hours—1520 mL

A. 11 mL/min

B. 63 mL/min

C. 95 mL/min

D. 106 mL/min

D. 106 mL/min

D. The creatinine clearance test is used to assess the glomerular filtration rate. An accurately timed 24-hour urine specimen and a blood sample, drawn in the middle of the 24-hour urine collection, are required. The creatinine concentrations of the urine specimen and the plasma are

determined, and these values, along with the urine volume, are used to determine the creatinine clearance. The body surface area will not be

used in the calculation because the clearance is being done on an average-size adult. The following general mathematical formula is used to calculate creatinine clearance:

(U/P) * V = Creatinine clearance (ml/min)

where U = urine creatinine concentration in milligrams per deciliter, P = plasma creatinine concentration in milligrams per deciliter, and V = volume of urine per minute, with volume expressed in milliliters and 24 hours expressed as 1440 minutes. Applying this formula to the problem presented in the question:

(120 mg/dL / 1.2 mg/dL) * (1520 mL/24hr / 1440 min/24hr)

= 106 mL/min

It should be noted that both the size of the kidney and the body surface area of an individual influence the creatinine clearance rate. Because normal values for creatinine clearance are based on the average adult body surface area, it is necessary that the clearance rate be adjusted when the body surface area of the individual being tested differs significantly from the average adult area. This type of adjustment is especially critical if the individual is an infant, a young child, or an adolescent. The body surface area may be calculated from an individual's height and weight, or it may be determined from a nomogram. The average body surface area is accepted as being 1.73 m2. The mathematical formula used to calculate a creatinine clearance when the body surface area of the individual is required follows:

(U/P) V (1.73 /A)= Creatinine clearance (mL/min/standard surface area)

where 1.73 = standard adult surface area in square meters and A = body surface area of the individual in square meters.

When it is not possible to perform a creatinine assay on a fresh urine specimen, to what pH level should the urine be adjusted?

A. 3.0

B. 5.0

C. 7.0

D. 9.0

C. 7.0

C. Creatinine assays are preferably performed on fresh urine specimens. If an acid urine specimen is kept for a time, any creatine in the urine will be converted to creatinine. In alkaline urine, an equilibrium situation will occur between the creatine and creatinine present in the specimen. To avoid either of these situations, it is recommended that the urine be adjusted to pH 7.0 and that the specimen be frozen. It is thought that at a neutral pH, the integrity of the urine specimen will be maintained because it will require days or even weeks for equilibrium to occur between the two compounds.

What compound normally found in urine may be used to assess the completeness of a 24-hour urine collection?

A. Urea

B. Uric acid

C. Creatine

D. Creatinine

D. Creatinine

D. Creatine is predominantly found in muscle cells, where the quantity of creatine is proportional to muscle mass. As muscle metabolism proceeds, creatine is freed from its high-energy phosphate form, and the creatine, thus liberated, forms the anhydride creatinine. The quantity of creatinine formed daily is a relatively constant amount because it is related to muscle mass. Therefore, it has been customary to quantify the creatinine present in a 24-hour urine specimen as an index of the completeness of the collection.

Which of the following reagents is not utilized in a coupled enzymatic reaction method to quantify serum creatinine?

A. Picric acid

B. Chromogenic dye

C. Creatinine amidohydrolase

D. Sarcosine oxidase

A. Picric acid

A. In addition to the endpoint and kinetic methods, which use the Jaffe reaction (picric acid), several methods have been developed that use coupled enzymatic reactions for the quantification of creatinine. In one such method, creatinine amidohydrolase (creatininase) catalyzes the conversion of creatinine to creatine and subsequently to sarcosine and urea. Sarcosine oxidase catalyzes the oxidation of sarcosine to glycine, formaldehyde, and hydrogen peroxide. The hydrogen peroxide reacts with the reduced form of a chromogenic dye in the presence of peroxidase to form an oxidized colored dye product that is read spectrophotometrically

An endogenous substance assayed to assess the glomerular filtration rate may be described as being filtered by the glomeruli, not reabsorbed by the tubules, and only secreted by the tubules when plasma levels become elevated. What is this frequently assayed substance?

A. Inulin

B. Uric acid

C. Creatinine

D. Urea

C. Creatinine

C. Creatinine is an endogenous substance that is filtered by the glomeruli and normally is neither reabsorbed nor secreted by the tubules. When plasma levels of creatinine rise, some secretion of creatinine by the tubules will occur. The filtration properties of creatinine and the fact that it is a substance normally present in blood make the creatinine clearance test the method of choice for assessing the glomerular nitration rate.

What is the end product of purine catabolism in humans?

A. Urea

B. Uric acid

C. Allantoin

D. Ammonia

B. Uric acid

B. Through a sequence of enzymatic reactions, the purine nucleosides, adenosine and guanosine, are catabolized to the waste product uric acid. The catabolism of purines occurs primarily in the liver, with the majority of uric acid being excreted as a urinary waste product. The remaining amount of uric acid is excreted in the biliary, pancreatic, and gastrointestinal secretions through the gastrointestinal tract. In the largeintestine, uric acid is further degraded by bacteria and excreted in the stool.

When mixed with phosphotungstic acid, what compound causes the reduction of the former to a tungsten blue complex?

A. Urea

B. Ammonia

C. Creatinine

D. Uric acid

D. Uric acid

D. Uric acid may be quantified by reacting it with phosphotungstic acid reagent in alkaline solution. In this reaction, uric acid is oxidized to allantoin and the phosphotungstic acid is reduced, forming a tungsten blue complex. The intensity of the tungsten blue complex is proportional to the concentration of uric acid in the specimen.

In the ultraviolet procedure for quantifying uric acid, what does the

reaction between uric acid and uricase cause?

A. Production of reduced nicotinamideadenine dinucleotide (NADH)

B. The formation of allantoin

C. An increase in absorbance

D. A reduction of phosphotungstic acid

B. The formation of allantoin

B. Uric acid absorbs light in the ultraviolet region of 290-293 nm. When uricase is added to a uric acid mixture, uricase destroys uric acid by catalyzing its degradation to allantoin and carbon dioxide. On the basis of these two characteristics, differential spectrophotometry has been applied to the quantification of uric acid. This type of method is used on analyzers that are capable of monitoring the decrease in absorbance as uric acid is destroyed by uricase. The decrease in absorbance is proportional to the concentration of uric acid in the specimen.