Clinical Chemistry and Renal Analysis Review

Flashcards covering clinical chemistry, spectrophotometry, quality control, Lean Six Sigma, method evaluation, renal physiology, and urinalysis.

What effect does EDTA have on potassium and calcium concentrations in blood samples?

EDTA binds to calcium, causing a false increase in measured potassium and a decrease in measured calcium.

What is an endpoint measurement in clinical laboratory testing?

A measurement designed to determine the amount of product (concentration) formed after a reaction has been allowed to proceed for a set period of time.

How does a kinetic measurement differ from an endpoint measurement?

Kinetic measurement involves continuous monitoring of the reaction over time to provide real-time data on the rate of product formation.

What does ISE stand for in laboratory analysis?

Ion selective electrode.

What are four clinical advantages of using ion selective electrodes (ISE)?

They are inexpensive, have a wide concentration measurement range, measure ion activity (useful for biological applications), and provide real-time measurement.

What additives are present in a Yellow-top tube, and what are its primary specimen testing uses?

Additives are SPS or ACD; specimen type is whole blood; used for blood cultures and microbial HLA studies.

What additive is inside a Pink-top blood collection tube, and what testing is performed with it?

EDTA additive; specimen type is whole blood (plasma); used for Blood Bank testing (grc/screen crossmatch).

What additives and specimen type are associated with a Gold tiger top tube?

Spray dried clot activator and polymer gel; specimen type is serum.

What additive is used in an Orange-top tube, and what is its primary application?

Thrombin and polymer gel; specimen type is serum; used for STAT chemistry testing.

What additives are found in a Gray-top tube, and what testing is performed using it?

Sodium fluoride with potassium oxalate OR EDTA; specimen type is plasma or serum; used for glucose, lactic acid, and blood alcohol testing.

What additive and fill ratio are required for a Light blue-top tube?

Liquid sodium citrate additive, requiring a strict $1:9$ ratio of anticoagulant to blood.

What additives are present in a White-top tube, and what is its primary application?

Polymer gel and spray-dried EDTA; specimen type is plasma; used for viral load testing and molecular diagnostics.

What is the primary function of polymer or thixotropic gel in blood collection tubes?

It migrates upward during centrifugation to physically separate formed blood elements from plasma or serum.

What additive is used specifically to preserve glucose in a blood specimen tube?

Sodium fluoride.

What tube color and additives are designated for blood culture testing in microbiology?

Blood culture bottle/tube containing SPS and culture media/nutrients.

How does overly diluting a calibrator affect quality control (QC) results?

Overly diluting the calibrator causes the calculated quality control results to read falsely high.

How does overly diluting a Quality Control (QC) sample affect its result?

Overly diluting the QC sample causes the QC result to read falsely low.

What is the interpretation of a $1_{2s}$ Westgard control rule violation?

One control observation exceeding the mean $\pm 2s$; it serves as a warning rule to initiate testing of control data by other rules.

What does a $1_{3s}$ Westgard rule violation indicate, and what action should be taken?

One control observation exceeding the mean $\pm 3s$; it indicates random error and requires rejecting patient results.

What type of analytical error does a $2_{2s}$ Westgard rule violation indicate?

Systematic error (two consecutive control observations exceeding the same mean $+ 2s$ or mean $- 2s$ limit).

What defines an $R_{4s}$ Westgard rule violation, and what type of error does it detect?

The range between two controls in the same run exceeds $4s$ (e.g., one QC is $+2s$ and the other is $-2s$); it detects random error.

What constitutes a $4_{1s}$ Westgard rule violation?

Four consecutive control observations exceeding the same mean $+ 1s$ or mean $- 1s$ limit, indicating systematic error.

What is a $10_x$ Westgard rule violation?

Ten consecutive control observations falling on one side of the mean (above or below), indicating a shift or systematic error.

How frequently should Internal Quality Control (IQC) be performed, and what action is required if results fall outside $\pm 2SD$?

Internal QC is performed daily; if results fall outside $\pm 2SD$, troubleshooting must be performed.

What is the purpose of baseline correction in spectrophotometry?

Running blank samples ensures the instrument reads zero absorbance before testing, eliminating background interference that causes falsely increased results.

What is the primary goal and focus of Lean methodology in a clinical laboratory?

The primary goal is to eliminate waste, focusing on speed, workflow, and turnaround time.

What is the primary goal and primary tool of Six Sigma methodology?

The primary goal is to eliminate defects and variation; the primary tool is statistical analysis (sigma, CV).

What are the 8 laboratory wastes represented by the acronym DOWNTIME in Lean methodology?

Defects, Overproduction, Waiting, Non-utilized talent, Transportation, Inventory, Motion, and Extra processing.

What defect-free percentage goal corresponds to world-class Six Sigma performance?

$99.99966\%$ defect-free test results.

What are the 5 sequential steps in the Six Sigma DMAIC process?

1. Define the problem 2. Measure current performance 3. Analyze the cause of defects 4. Improve the process 5. Control the new process.

What percentage of overall laboratory errors impact patient health?

$12\%$ of laboratory errors impact patient health.

What percentage of clinical laboratory errors occur specifically in the analytical stage?

$0.0375\%$ of errors occur in the analytical stage.

How many errors per million tests are produced by a 6 Sigma process compared to a 3 Sigma process?

A 6 Sigma process produces 3 errors per million tests, whereas a 3 Sigma process produces 26,674 errors per million tests.

What happens to the calculated Sigma metric score if the coefficient of variation (CV) of an assay increases?

Sigma decreases, indicating the assay has become less reliable.

What happens to the calculated Sigma metric score if assay bias is improved and moves closer to the target?

Sigma increases, indicating the test has become more accurate.

What is the key laboratory metric monitored in Lean methodology?

Turnaround time (TAT).

What is the key laboratory metric monitored in Six Sigma methodology?

Sigma metric score.

What primary tool is utilized in Lean methodology to optimize laboratory process flow?

Workflow mapping.

What key test characteristics must be evaluated during method selection for a clinical analyzer?

Analytic sensitivity, analytic specificity, linear range, interfering substances, and estimates of precision and accuracy.

What three types of specific studies are conducted to determine method accuracy?

Recovery studies, interference studies, and PT (patient) sample comparison studies.

How is a recovery study performed in clinical method evaluation?

By adding a spiked sample to a patient sample and measuring analyte recovery to determine detection in the presence of matrix compounds (original sample dilution must not exceed $10\%$).

What are three common endogenous interferents tested during interference studies?

Hemolysis, bilirubin, and lipemia.

What protocol is required for a patient sample comparison study during method evaluation?

Run 40 to 100 specimens on both evaluation and reference methods on the same day over 8 to 20 days (preferably within 4 hours), analyzed in duplicate.

What does the correlation coefficient ($r$) measure in method comparison statistics?

It defines the strength of the linear relationship between two variables, ranging from $-1$ to $+1$.

What does the coefficient of determination ($r^2$) represent in regression analysis?

It indicates how well the regression line represents the comparative data.

How is carryover testing performed on an automated clinical chemistry analyzer?

By testing a specimen with a high known result followed immediately by a specimen with a very low or negative result to see if the second result is falsely elevated.

How is a standard reference interval defined with respect to healthy individuals?

It is designed so that $95\%$ of healthy patients fall within the upper and lower limits.

How many healthy patient samples are required to verify an existing reference interval when adopting a new method?

As few as 40 samples (compared to 120 required to establish a brand-new interval).

What is the mathematical formula for Diagnostic Sensitivity?

$$\text{Diagnostic Sensitivity} = \frac{\text{TP}}{\text{TP} + \text{FN}}$$

What is the mathematical formula for Diagnostic Specificity?

$$\text{Diagnostic Specificity} = \frac{\text{TN}}{\text{TN} + \text{FP}}$$

What is Positive Predictive Value (PPV), and what is its mathematical formula?

PPV is the probability that a patient has the disease when the test result is abnormal; $\text{PPV} = \frac{\text{TP}}{\text{TP} + \text{FP}}$.

What is Negative Predictive Value (NPV), and what is its mathematical formula?

NPV is the probability that a patient does not have the disease when the test result is within the reference interval; $\text{NPV} = \frac{\text{TN}}{\text{TN} + \text{FN}}$.

What six conditions dictate when an instrument should be recalibrated?

1. Routine schedule 2. After maintenance or repairs 3. Introduction of new reagent batches 4. Questionable patient results 5. Manufacturer guidance 6. Trends/shifts in Quality Control data.

What physical law forms the theoretical basis for two-point linear calibration curves in spectrophotometry?

Beer-Lambert's Law.

What impact do calibration curve errors have on Internal Quality Control (IQC) values?

Deviations in calibration curves cause significant shifts in IQC values and lead to incorrect calculation of unknown patient sample concentrations.

What are four common operational causes of calibration shifts?

Incorrect reconstitution of calibrators, expired calibrator material, reagent contamination, and altered reagent performance.

What must be done if a test method fails to meet allowable analytical error criteria?

The testing method must be modified or rejected.

What is the basic definition of spectrophotometry?

A quantitative analytical technique that measures how much light a chemical substance absorbs or transmits at specific wavelengths.

State Beer-Lambert's Law formula and define each constituent variable.

$A = \epsilon l c$ where $A$ is absorbance (unitless), $\epsilon$ is molar absorptivity constant, $l$ is light path length (typically $1\,\text{cm}$), and $c$ is solute concentration ($\text{mol/L}$).

What is the primary chemical limitation of Beer-Lambert's Law?

It applies only to dilute solutions, because higher solute concentrations cause electrostatic interactions between molecules that lead to non-linear deviations.

What specific light source lamps are used in spectrophotometers for visible light versus ultraviolet (UV) light?

Tungsten lamps for visible light ($320\text{ to }1000\,\text{nm}$) and deuterium lamps for ultraviolet light ($190\text{ to }320\,\text{nm}$).

What is the structural component and function of a monochromator in a spectrophotometer?

It uses a prism or diffraction grating with entrance/exit slits to isolate a narrow band of wavelengths from the broadband light source.

What optical function does a collimator perform?

It is a lens or mirror that converts diverging light rays from the source into a parallel beam.

What cuvette materials are required for measurements taken in the visible range versus the UV range?

Glass or plastic for the visible light range; quartz or silica for the UV light range.

What detector devices convert transmitted light into an electrical signal in spectrophotometry?

Photodiodes or photomultiplier tubes (PMT).

What visible spectrum wavelengths correspond to violet/blue light versus red light?

Violet/blue light has shorter wavelengths ($400\text{--}500\,\text{nm}$); red light has longer wavelengths (approx. $700\,\text{nm}$).

Is percent transmittance ($\%T$) directly proportional to solute concentration?

No, transmitted light is not directly proportional to concentration and does not produce a straight line on a linear graph.

What is the mathematical equation relating Absorbance ($A$) to percent transmittance ($\%T$)?

$$A = -\log\left(\frac{I}{I_0}\right) = 2 - \log(\%T)$$

How is stray light defined in spectrophotometry?

Any wavelength outside the narrow band transmitted by the monochromator.

What effect does stray light have on observed sample absorbance readings?

Stray light alters sample absorbance, causing the observed absorbance reading to be falsely lower than the true value.

How is wavelength accuracy QC performed on a spectrophotometer?

It is checked using reference standards or filters with maximum absorbance at a known wavelength (e.g., holmium oxide or potassium dichromate).

What formula calculates total protein concentration in unknown samples using a single calibrator standard?

$\text{Total protein concentration} = \frac{A \times A_c}{\text{concentration of calibrator}}$ where $A$ is absorbance of unknown and $A_c$ is absorbance of calibrator.

How does the light path differ between absorbance spectrophotometry and reflectance spectrophotometry?

In absorbance spectrophotometry, light is transmitted through the sample; in reflectance spectrophotometry, light is reflected/scattered off the sample surface.

What is the difference between specular reflection and diffuse reflection?

Specular reflection occurs on smooth surfaces where angle of reflection equals angle of incidence; diffuse reflection occurs on rough surfaces where light scatters in many directions.

What clinical instruments and applications utilize reflectance spectrophotometry?

Point-of-care (POCT) devices like glucose monitors, urinalysis instruments using dry reagents, and the Vitros chemistry platform.

What sample types are analyzed by reflectance spectrophotometry compared to absorbance spectrophotometry?

Reflectance analyzes solids, powders, rough surfaces, and dry coatings; absorbance analyzes liquids, solutions, gases, and thin films.

What are the four primary analytical disciplines under which laboratory techniques fall?

1. Spectrometry 2. Luminescence 3. Electro-analytic methods 4. Chromatography.

State Planck's formula relating electromagnetic energy to wavelength and frequency.

$E = h \nu$ where $E$ is photon energy, $h$ is Planck's constant ($6.62 \times 10^{-27}\,\text{erg\,sec}$), and $\nu = \frac{1}{\lambda}$ is frequency.

What optical filters are used to check spectrophotometer linearity across different wavelengths?

Neutral density filters.

What feature on a reflectance spectrum indicates light absorption by a sample?

Dips in the reflectance spectrum (percentage of light reflected at specific wavelengths) indicate absorption.

What is the clinical purpose of the urine protein-to-creatinine ratio (UPCR) test?

It measures total protein and creatinine in a random urine sample to correct for hydration status and screen for proteinuria or glomerular kidney damage.

What are normal UPCR reference values for men and women?

Men: $0.148\,\text{mg/mg}$ creatinine or less; Women: $0.184\,\text{mg/mg}$ creatinine or less.

What UPCR value defines the nephrotic range?

UPCR $> 3.0\,\text{mg/mg}$, indicating significant renal protein loss.

What microscopic powers are used for examining urine sediment, and what elements are evaluated at each?

Low power ($10\times$) scans for casts and crystals; high power ($40\times$) evaluates RBCs, WBCs, and epithelial cells.

What microscopic counts for RBCs and WBCs in urine sediment are considered abnormal?

RBC $> 2\,\text{per HPF}$ and WBC $> 5\,\text{per HPF}$ are abnormal.

What specific protein matrix forms urinary casts during renal tubular stasis?

Tamm-Horsfall protein.

List three urine crystals seen in acidic urine (pH < 7) and three seen in alkaline urine (pH > 7).

Acidic urine: Calcium oxalate, amorphous urates, uric acid; Alkaline urine: Amorphous phosphates, calcium carbonate, triple phosphate.

Name four pathological urine crystals.

Leucine, tyrosine, cystine, and sulfonamides (or cholesterol/bilirubin).

What is the relative abundance of urea among NPN compounds in blood plasma and urine?

Urea accounts for $45\text{--}50\%$ of total plasma NPN and $86.0\%$ of excreted urinary nitrogen.

Where and from what metabolic precursors is urea synthesized in the human body?

Synthesized in the liver from amino groups ($\text{-NH}_2$) and free ammonia generated during protein catabolism via the urea cycle.

What is the adult reference range for Blood Urea Nitrogen (BUN) in plasma/serum?

$6\text{--}20\,\text{mg/dL}$ ($2.1\text{--}7.1\,\text{mmol/L}$).

What chemical equations describe the coupled enzymatic GLDH reaction sequence for urea assay?

First step catalyzed by urease: $\text{Urea} + 2\text{H}_2\text{O} \rightarrow 2\text{NH}_4^+ + \text{CO}_3^{2-}$; Second step catalyzed by GLDH: $\text{NH}_4^+ + 2\text{-oxoglutarate} + \text{NADH} + \text{H}^+ \rightarrow \text{glutamate} + \text{NAD}^+ + \text{H}_2\text{O}$.

Why must collection tubes containing high sodium citrate or sodium fluoride be avoided for enzymatic urea assays?

High concentrations of sodium citrate and sodium fluoride inhibit the enzyme urease.

Differentiate between Azotemia and Uremia.

Azotemia is an elevated concentration of urea/NPN compounds in blood; Uremia is elevated plasma urea accompanied by renal failure and systemic clinical symptoms.

What metabolic breakdown produces uric acid, and what clinical pathology results from hyperuricemia?

Uric acid is the end product of purine nucleic acid catabolism; hyperuricemia causes precipitation of monosodium urate crystals in joints, resulting in gout.

What is the adult plasma/serum reference range for uric acid in males versus females?

Males: $3.5\text{--}7.2\,\text{mg/dL}$ ($0.21\text{--}0.43\,\text{mmol/L}$); Females: $2.6\text{--}6.0\,\text{mg/dL}$ ($0.16\text{--}0.36\,\text{mmol/L}$).

What chemical reaction is traditionally used to measure creatinine, and what color complex is formed?

Jaffe reaction: creatinine reacts with alkaline picrate to form a red-orange chromogen complex.

Name two substances that cause a positive bias and one that causes a negative bias in Jaffe creatinine assays.

Positive bias: $\alpha$-keto acids, cephalosporins, glucose, and ascorbate; Negative bias: bilirubin.

What pre-analytical handling steps are required for accurate plasma ammonia testing?

Draw venous blood without trauma, place on wet ice immediately, centrifuge cold ($0\text{--}4\,^\circ\text{C}$) within 20 minutes, separate plasma from cells, test immediately/freeze, and instruct patient not to smoke prior to collection.

What is the adult reference range for plasma ammonia?

$19\text{--}60\,\mu\text{g/dL}$ ($11\text{--}35\,\mu\text{mol/L}$).