BOC LAB OP

A patient sample was delayed in transit to the lab, resulting in a falsely elevated potassium level. What type of variable is this?

Pre-analytical variable (occurs before the actual testing phase begins)

What is the formula for the Coefficient of Variation (CV%)?

(Standard Deviation / Mean) * 100

If an instrument runs the same control sample 10 times and yields tightly clustered but highly inaccurate results, how is its performance described?

High precision, low accuracy

What percentage of control values are expected to fall within \(\pm 2\) standard deviations (2s) in a normal Gaussian distribution?

95% (Values outside of this range often trigger QC flags or Westgard rule rejections)

Define diagnostic specificity in the clinical laboratory.

The ability of a test to produce a negative result if the patient truly does not have the disease

What is the formula for calculating the Standard Deviation Index (SDI), and what is the acceptable limit?

SDI = (Your Lab's Result - Group Mean) / Group Standard Deviation

An acceptable SDI value should be less than 2

What is a Delta Check, and what action must you take if a sample fails a Delta Check?

A comparison of a patient's most recent test result with their previous result(s). If it fails due to a large disparity, the immediate action is to rerun both samples to rule out mislabeling or pre-analytical error

In method comparison, what parameters do the t-test and F-test evaluate?

• t-test: Compares means; evaluates accuracy.

• F-test: Compares standard deviations; evaluates precision

How do you differentiate between random error and systematic error causes?

• Random: Unpredictable; caused by voltage fluctuations, bubbles in line, or incorrect sample volume.

• Systematic: Directional bias; caused by an incorrect y-intercept/slope, dirty photometers, or decomposed standards.

Front: What percentage of a healthy, random population is expected to fall within a standard normal reference range (± 2s)?

95% of the population

Which Westgard rule is strictly a warning rule, and what action should the technician take if it is triggered

1_2s (one control value exceeds ± 2s).

If no other Westgard rules are broken, you accept the patient results and look for trends.

Which Westgard multi-rules primarily indicate an out-of-control run due to random error?

1_3s: One control observation exceeds ± 3s.

R_4s: One control exceeds +2s and the very next (or other control in the run) exceeds -2s, putting them > 4s apart.

Which Westgard multi-rules primarily indicate an out-of-control run due to systematic error?

2_2s: Two consecutive controls exceed the same +2s or -2s limit.

4_1s: Four consecutive controls exceed the same +1s or -1s limit.

10_x: Ten consecutive controls fall on one side of the mean.

How do you visually differentiate a trend from a shift on a Levey-Jennings chart?

• Trend: Values gradually, continuously increase or decrease over 6 consecutive days.

• Shift: Values abruptly distribute themselves on one side of the mean line for 6 or more consecutive days.

What are the classic laboratory troubleshooting causes for a trend versus a shift?

• Trend Causes: Deteriorating reagents or gradual instrument wear.

• Shift Causes: Deterioration of a standard, abrupt change in reagent lot, or sudden light source/component failure.

What is the definition of the Analytical Measurement Range (AMR)?

The range of analyte values a procedure can measure directly without any dilution, concentration, or other pretreatment

What is the minimum number of healthy individuals required to establish a new reference range for a laboratory analyte?

A minimum of 100 individuals from the community served by the laboratory.

To determine the 95% confidence limits (± 2s) for a reference range, what type of statistical distribution must the analyte values follow?

A Gaussian (normal) distribution

Which type of concentration measurement (w/w, w/v, or v/v) is most commonly used in the clinical laboratory when mixing a solid solute with a liquid solvent?

Weight per unit volume (w/v). (e.g., 1% = 1 g / 100 mL).

What is the correct protocol for preparing a liquid solution involving concentrated acid and water, and why?

Always add Acid to Water (A&W).
Never add water to acid, as the extreme heat generated can cause the solution to boil and splash acid violently

What term describes physiological changes in analyte concentration that vary depending on the time of day, and what is a classic exam example?

Diurnal variation.
Classic examples include cortisol (peaks in early morning) and iron

What formula is used to calculate changes in solution concentration or volume when diluting a stock solution?

V1 x C1 = V2 x C2

(Where V = Volume and C = Concentration. Units on both sides must match).

What is the definition of Molarity (\(M\)), and what are its standard volume units?

Molarity expresses the number of moles of solute per 1 Liter (1000 mL) of solution.

M = moles / Liter

What is the formula used to find the number of grams needed to prepare a solution of a specific molarity and volume?

Grams needed = Molarity (M) x Gram Molecular Weight (GMW) x Volume in Liters (L)

When a problem asks you to scale a solution up or down without changing its percentage concentration, what algebraic method is quickest?

The ratio-proportion cross-multiplication method:

(unit weight 1) / (unit volume 1) = (unit weight 2) / (unit volume 2)

What are the approximate Gram Molecular Weights (GMW) of NaCl and H2SO4? (Highly useful to memorize for speed during the exam)

NaCl: 58.5 g/mol (Na = 23, Cl = 35.5)

H2SO4: 98 g/mol (H = 1x2, S = 32, O = 16x4)

What is the formula to convert Molarity (M) to Normality (N)?

N = M x valence

(Valence is the number of exchangeable hydrogen or hydroxyl ions, or the absolute ion charge).

What is the formula for Gram Equivalent Weight (GEW)?

GEW = Gram Molecular Weight (GMW) / valence

What is the calculation formula to convert a clinical lab value from mg/dL to mEq/L?

mEq/L = (mg/dL x 10) / GEW

In clinical chemistry reporting, what standard concentration unit is exactly equivalent to "mg%"?

mg/dL (milligrams per deciliter)

What is the valence (total positive charge or replaceable H+) of Na2SO4, H2SO4, and H3PO4?

Na2SO4: 2 (Two Na+ ions)

H2SO4: 2 (Two H+ ions)

H3PO4: 3 (Three H+ ions)

What is the specific mathematical formula used to calculate Absorbance (A) when given Percent Transmittance (%T)?

2 - log %T

According to Beer's Law, what is the mathematical relationship between the light absorbed (A) by a solution and its concentration (c)?

They are directly proportional.
As the concentration of the substance increases, the absorbance increases linearly.

What three hardware components can be used in a spectrophotometer to select a narrow wavelength range of light?

Prisms, gratings, or filters.

How many microliters (µL) are in one milliliter (mL)?

1000 µL = 1 mL (or 1 µL = 0.001 mL).

List the metric prefixes for 10^-3, 10^-6, 10^-9, and 10^-12 in order.

10^-3 = Milli (m)

10^-6 = Micro (µ)

10^-9 = Nano (n)

10^-12 = Pico (p)

What is the formula to calculate the concentration of an unknown patient sample using a known standard?

Concentration of Unknown = (Absorbance of Unknown / Absorbance of Standard) x Concentration of Standard

Which light sources are used for the visible and ultraviolet (UV) ranges in a spectrophotometer?

• Visible range: Tungsten lamp

• Ultraviolet (UV) range: Deuterium or Hydrogen discharge lamp

 What specific filters or materials are used to check the wavelength calibration and accuracy of a spectrophotometer?

Holmium oxide or Didymium filters

What causes a deviation from Beer's Law via stray light, and how is it detected?

Stray light is any light outside the selected wavelength reaching the detector. It is detected using sharp cutoff filters/solutions (like Nickel Sulfate, NiSO4)

What is bichromatic analysis, and why is it used in automated chemistry analyzers?

An automation method where absorbance is measured at two different wavelengths to minimize interferences caused by specimen turbidity, hemolysis, or icterus

In fluorometry, how do the wavelength and energy of the emitted light compare to the absorbed light?

Emitted light has a longer wavelength and lower energy

What is the principle of nephelometry, and at what angle is the light measured?

It measures light scattered by antigen-antibody complexes at a 90° angle to the incident beam

What does turbidimetry measure compared to nephelometry?

Turbidimetry measures the amount of light blocked (decreased transmission) by particulate matter in a straight line

What four properties change when the number of dissolved particles in a solution increases?

• Freezing point decreased

• Vapor pressure decreased

• Boiling point increased

• Osmotic pressure increased

Why must you use freezing point depression instead of vapor pressure osmometry to detect alcohol toxicity?

Volatile solutes (like ethanol or methanol) escape during heating in vapor pressure osmometry. They are only detected by freezing point depression

What methodology serves as the gold standard confirmatory test for regulated drugs of abuse?

Chromatography-Mass Spectrometry (GC-MS)

What two primary physical properties determine how proteins separate during standard electrophoresis?

Ionic charge and molecular size.

What is the most commonly used support medium for routine clinical electrophoresis?

Cellulose acetate

What is the mathematical formula used to determine the Retention Factor (Rf) in chromatography?

Distance moved by constituent / Distance moved by solvent

In High-Performance Liquid Chromatography (HPLC), what does a noisy baseline or drifting baseline typically indicate?

• Noisy baseline: Bubbles or particulate matter in the flow cell.

• Drifting baseline: Column overloading or temperature changes

What are the two most likely causes of crescent-shaped protein bands on an electrophoresis gel?

Overloading the sample or using a bent applicator

What specific liquid ionophore substance is used in the membrane of a potassium ion-selective electrode?

Valinomycin

What does potentiometry measure, and what are two classic laboratory examples?

It measures a change in voltage (potential) between an indicator and a reference electrode when no current is flowing.

Examples include pH meters and electrolyte ISEs.

What type of electrochemistry does a pO2 electrode use, and what metals make up its cathode and anode?

It uses amperometry (measuring current).
It features a platinum cathode and a silver/silver chloride (Ag/AgCl) anode

What is the principle of coulometry, and what clinical analyte is historically measured by this titration method?

A titration method where the titrant (silver ions) is electrochemically generated, measuring the length of time it takes to consume the analyte. It is used to measure Chloride (Cl-).

In flow cytometry and optical scatter methodologies, what cellular characteristic does forward light scatter measure?

Cell size (volume)

In flow cytometry and optical scatter methodologies, what cellular characteristic does right angle (side) light scatter measure?

Internal complexity (interior cell structure, including the presence of a nucleus and granules).

Under the electronic impedance (Coulter) principle, what does the size/height of the electrical pulse represent?

The size (volume) of the cell passing through the aperture

Which red blood cell index is directly measured by the pulse sizes in a standard electronic impedance analyzer?

MCV (Mean Cell Volume)

How are red blood cells handled in the WBC counting bath during electronic impedance analysis to avoid false high counts?

The RBCs are completely lysed in the WBC bath so that only white blood cells and nucleated RBCs (if present) are counted

What clinical scenario is classically indicated by a bimodal (dual peak) curve on an automated RBC histogram?

An iron-deficiency anemia or microcytic anemia patient who recently received a blood transfusion (showing both patient and donor cells)

What two primary pre-analytical or morphological anomalies cause an R1 flag on an automated WBC histogram?

Nucleated RBCs (nRBCs) or platelet clumps

What abnormal cells are typically responsible for triggering an R2 flag on a 3-part differential histogram?

Blasts, immature granulocytes, or variant (reactive) lymphocytes

What do the letters in Beckman Coulter's VCS technology scattergram parameter stand for?

• V = Volume (impedance)

• C = Conductivity (internal cell composition)

• S = Scatter (surface characteristics/laser light scatter)

Beyond light scatter, what specific chemical stain does the Siemens Advia instrument utilize to differentiate white blood cell populations?

Peroxidase staining

What characteristically happens to the RBC, MCV, and MCHC in the presence of cold agglutinins, and how is it corrected?

RBC: Falsely decreased

MCV & MCHC: Falsely increased

Correction: Warm the specimen to 37°C in a water bath and immediately re-analyze.

What three major specimen or patient anomalies cause a falsely elevated automated Hemoglobin and MCHC result?

Lipemia, icterus (hyperbilirubinemia), and an extremely high WBC count (leukocytosis)

How do platelet clumps or giant platelets affect automated WBC and platelet counts?

They cause a falsely decreased platelet count and a falsely increased WBC count (because the instrument sizes the clumps as white blood cells)

Why is electromechanical clot detection preferred over photo-optical clot detection for lipemic, icteric, or hemolyzed coagulation samples?

Electromechanical methods measure physical movement (e.g., an iron ball) and are completely unaffected by sample turbidity or color changes

What analytical methodology and byproduct gas do automated blood culture systems use to detect positive bacterial growth?

They use infrared spectrophotometry to detect an increase in CO2 gas produced by the organisms.

Which electrophoresis variant is specifically used in epidemiology for sub-species bacterial typing and outbreak investigation?

Pulsed-Field Gel Electrophoresis (PFGE)

 In what units does a luminometer report the light intensity produced during a chemiluminescent assay?

Relative Light Units (RLU) (which are directly proportional to the amount of bound/hybridized probe or analyte)

What are three non-invasive sensor mechanisms used by automated blood culture systems to detect the CO2 index?

• Infrared spectrophotometry

• Internal pH indicators imbedded in the bottles

• Fluorescent sensors

In automated systems like MicroScan or VITEK, what physical state are the biochemical and antimicrobial reagents in prior to sample inoculation?

They are desiccated (freeze-dried) inside the wells and become rehydrated when the liquid bacterial suspension is added

What three primary optical methods are utilized by automated bacteriological instruments to determine well reactions?

Turbidity, colorimetry, and fluorescence

On what specific physical property does MALDI-TOF separate ionized molecules to identify microorganisms?

The mass-to-charge ratio (m/z) of the molecules

What type of cellular biomolecules does MALDI-TOF primarily analyze to create a spectral fingerprint for organism identification?

Proteins (specifically highly abundant ribosomal proteins)

What is the primary operational advantage of Real-time PCR platforms over traditional PCR methods?

It amplifies and detects nucleic acids simultaneously, shortening turnaround time to under an hour

What optical methodology is utilized by automated urinalysis analyzers to read chemical reagent strips?

Reflectance photometry

What three technological methods do automated urinalysis instruments use to identify and quantify cellular elements in urine sediment?

Flow cytometry, digital imaging, or automated particle recognition

In flow cytometry, what is the primary operational purpose of the sheath fluid inside the flow cell?

It uses pressure to hydrodynamically focus the sample stream so cells pass through the laser beam in a single-file line

What type of laser and specific wavelength is standard in routine clinical flow cytometry analyzers?

An Argon gas laser emitting light at 488 nm

What two optical physics phenomena are responsible for creating forward light scatter signals?

Diffraction (light bending around edges) and refraction (light bending through the cell body)

What specific optical physics phenomenon allows right-angle (side) scatter to detect cellular granules?

Reflection (light bouncing off internal cell components and granules)

What does the term "gating" mean when interpreting automated flow cytometry scattergram data?

The electronic selection of a specific population of cells on a plot to isolate them for further analysis.

Which specific cluster of differentiation (CD) marker is expressed on all white blood cells and used for gating leukocyte populations in flow cytometry?

CD45

Which two CD markers must be evaluated to calculate the helper/suppressor ratio in a patient being monitored for HIV?

CD4 (T helper lymphocytes) and CD8 (T suppressor/cytotoxic lymphocytes)

What is the primary function of an isotypic control in automated flow cytometry analysis?

To identify and correct for non-specific background staining and antibody binding to Fc receptor sites. It is used to adjust instrument gains to define 1% baseline positivity

What are the standard emission colors and wavelengths for the direct fluorochromes FITC and PE when excited at 488 nm?

• FITC: Green color emission (500–530 nm)

• PE: Yellow color emission (550–590 nm)

Why must an acid-based lysis reagent be added to an immunophenotyping blood sample before running it through a flow cytometer?

To eliminate red blood cells (RBCs) so they do not crowd or interfere with white blood cell counting and signal acquisition

What is the formula used to calculate the absolute count of a specific lymphocyte subset (e.g., CD3+ cells) from flow cytometry data?

Absolute Count = % positive cells x % lymphocytes x Total WBC

(All percentages must be converted to decimal format first).

What is the "Lymphosum" quality control equation, and what is its acceptable variance range?

% T cells (CD3) + % B cells (CD19) + % NK cells (CD16+56) = 100% ± 5%

What mathematical relationship must exist between CD3, CD4, and CD8 percentages to pass internal quality control validation?

The total % CD3 must equal the sum of % CD4 + % CD8 within a margin of ± 5%

What are the minimum acceptable percentages for sample gate Purity and gate Recovery in immunophenotyping?

Purity: Must equal or exceed 90%

Recovery: Must equal or exceed 95%

To be properly classified and counted as a helper T lymphocyte during T-gating analysis, which two specific CD antigens must the cell express simultaneously?

It must co-express both CD3 and CD4

What specific absolute CD4+ T-lymphocyte count defines the clinical onset of AIDS in an HIV-positive patient?

A CD4+ count below 200/µL (or 200/mm3)

At what absolute CD4+ count threshold should medical teams initiate opportunistic infection prophylaxis in an HIV patient?

When the count drops below 500/µL.

What is the standard physiological reference range for an absolute CD4+ count in a healthy adult?

450 to 1500/µL.

What specific internal quality control material must be added to a sample tube to perform single-platform absolute cell counting?

Flow cytometry calibration beads