Medical Laboratory Technician (MLT) Exam — Questions and Answers

Question 1: A technologist must prepare a 1:5 dilution of a patient's serum in saline to perform a test. If the final volume needed is 1.0 mL (1000 µL), how much patient serum should be used?

800 µL
500 µL
200 µL (Correct answer)
100 µL

Correct answer: 200 µL

A 1:5 dilution means 1 part solute (serum) plus 4 parts diluent (saline) for a total of 5 parts. To calculate the amount of serum needed, divide the final volume by the dilution factor: 1000 µL / 5 = 200 µL. The technologist would then add 800 µL of saline to the 200 µL of serum to achieve the final volume of 1000 µL.

Question 2: The term 'analytical sensitivity' in laboratory testing refers to:

The proportion of disease-positive patients with a positive test result
The ability of the test to avoid false-positive results
The lowest detectable concentration of an analyte (Correct answer)
The agreement between two testing methods

Correct answer: The lowest detectable concentration of an analyte

Analytical sensitivity is the lowest analyte concentration reliably detected by the assay, also called the limit of detection.

Question 3: A patient's liver function panel shows a significantly elevated Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST), with an AST:ALT ratio greater than 2:1. Gamma-glutamyl transferase (GGT) is also markedly elevated. This pattern is most suggestive of:

Non-alcoholic fatty liver disease
Cholestatic liver injury
Viral hepatitis
Alcoholic liver disease (Correct answer)

Correct answer: Alcoholic liver disease

An AST to ALT ratio of 2:1 or greater, especially in conjunction with a significantly elevated GGT, is a classic indicator of alcohol-induced liver injury.

Question 4: A mercury thermometer breaks on the laboratory bench. What is the correct first response?

Pour water over the spill to prevent evaporation
Wipe it up with paper towels and discard in regular trash
Evacuate the immediate area and use a mercury spill kit (Correct answer)
Vacuum the mercury with a standard vacuum cleaner

Correct answer: Evacuate the immediate area and use a mercury spill kit

Mercury spills require evacuation of the immediate area and cleanup using a specialized mercury spill kit to prevent toxic vapor inhalation.

Question 5: Which blood type is considered the universal plasma donor?

AB (Correct answer)
A
B
O

Correct answer: AB

Type AB plasma lacks both anti-A and anti-B antibodies, making it safe for transfusion to any recipient.

Question 6: During an antibody identification panel, a technologist notices that all panel cells positive for the Jka antigen are reactive. The autocontrol is negative. Which additional test would best confirm anti-Jka?

Neutralization with soluble Jka substance
Enzyme-treated panel cells (Correct answer)
Ficin-treated panel cells to destroy Jka antigen
Cord blood cells

Correct answer: Enzyme-treated panel cells

Kidd antibodies are enhanced by enzyme treatment, so enzyme-treated panel cells would strengthen the reactions and help confirm anti-Jka.

Question 7: Which irradiation dose is used for blood components to prevent transfusion-associated graft-versus-host disease (TA-GvHD)?

2,500 cGy minimum (Correct answer)
5,000 cGy
1,500–2,000 cGy
500–1,000 cGy

Correct answer: 2,500 cGy minimum

A minimum of 2,500 cGy (25 Gy) delivered to the midplane inactivates donor lymphocytes and prevents TA-GvHD.

Question 8: A patient with anti-K antibody needs a transfusion. Which percentage of random donors are Kell-negative?

About 50%
About 99%
About 9%
About 91% (Correct answer)

Correct answer: About 91%

Approximately 91% of the population is K-negative (kk genotype), making compatible blood relatively easy to find.

Question 9: What is the purpose of running quality control samples at two different concentration levels in clinical chemistry?

To verify accuracy across the reportable range of the assay (Correct answer)
To determine the reference range for the analyte
To calibrate the instrument before patient testing
To identify the detection limit of the method

Correct answer: To verify accuracy across the reportable range of the assay

Running QC at two levels (normal and abnormal) ensures the assay performs accurately across the clinically relevant measurement range.

Question 10: Which coagulation factor is measured exclusively by the prothrombin time (PT) and not the activated partial thromboplastin time (aPTT)?

Factor V
Factor VII (Correct answer)
Factor X
Factor II

Correct answer: Factor VII

Factor VII is unique to the extrinsic pathway and is evaluated only by the PT.

Question 11: A patient receiving a red blood cell transfusion develops fever, chills, and hypotension 30 minutes into the infusion. The post-transfusion plasma appears pink. Which action should the technologist perform FIRST after the transfusion is stopped?

Return the blood bag and all attached tubing to the blood bank with a new post-transfusion blood sample (Correct answer)
Perform a direct antiglobulin test (DAT) on the pre-transfusion sample
Repeat the ABO typing on the original donor unit
Issue O-negative blood for an emergency transfusion

Correct answer: Return the blood bag and all attached tubing to the blood bank with a new post-transfusion blood sample

When an acute hemolytic transfusion reaction is suspected, the blood bag with all attached tubing and a new post-transfusion sample must be returned to the blood bank immediately. This allows comparison of pre- and post-transfusion specimens, visual inspection for hemolysis, and repeat compatibility testing—the foundational steps of a transfusion reaction workup.

Question 12: Which of the following is the most appropriate product for a neonate requiring an exchange transfusion for hemolytic disease of the fetus and newborn (HDFN) caused by anti-D?

Mother's own red blood cells, washed
Group O, Rh-positive red blood cells in saline
Group-specific Rh-negative whole blood
Group O, Rh-negative red blood cells resuspended in AB plasma (Correct answer)

Correct answer: Group O, Rh-negative red blood cells resuspended in AB plasma

Group O Rh-negative RBCs avoid ABO and Rh incompatibility, and AB plasma lacks anti-A and anti-B antibodies that could harm the neonate's cells.

Question 13: Which anticoagulant is preferred for routine coagulation testing such as PT and aPTT?

Potassium oxalate
EDTA
Sodium heparin
3.2% sodium citrate (Correct answer)

Correct answer: 3.2% sodium citrate

Sodium citrate at 3.2% concentration is the standard anticoagulant for coagulation studies because it reversibly binds calcium.

Question 14: Which type of fire extinguisher is appropriate for a Class B fire involving flammable liquids such as ethanol or acetone in a laboratory?

Class A water extinguisher
Class D dry powder extinguisher
Class ABC dry chemical or Class BC carbon dioxide extinguisher (Correct answer)
Class C carbon dioxide extinguisher only

Correct answer: Class ABC dry chemical or Class BC carbon dioxide extinguisher

Class B fires involve flammable liquids. A Class ABC dry chemical extinguisher or a Class BC carbon dioxide (CO₂) extinguisher are appropriate for these fires. A water extinguisher (Class A) can spread flammable liquids, and a Class D extinguisher is reserved for combustible metals.

Question 15: During ABO blood typing, a patient's forward type shows agglutination with anti-B reagent only, and the reverse type shows agglutination with A1 cells only. What is the patient's blood type?

Type B (Correct answer)
Type AB
Type A
Type O

Correct answer: Type B

Agglutination with anti-B in forward typing indicates B antigen on red cells, and agglutination with A1 cells in reverse typing confirms anti-A in the serum, consistent with type B.

Question 16: A new method is being compared to the current reference method using patient samples. Which statistical parameter best expresses the average difference in results between the two methods?

Bias (Correct answer)
Correlation coefficient (r)
Coefficient of variation (CV)
Standard deviation (SD)

Correct answer: Bias

Bias is the systematic difference between the mean result of a new method and the mean result of the reference method. While the correlation coefficient shows how linearly related the two methods are, it does not reveal whether one method reads higher or lower than the other — bias quantifies that difference directly.

Question 17: A patient's blood glucose level is 250 mg/dL with ketonuria present. Which condition is most likely?

Cushing syndrome
Diabetic ketoacidosis (Correct answer)
Hypoglycemia
Addison disease

Correct answer: Diabetic ketoacidosis

Elevated blood glucose combined with ketonuria is characteristic of diabetic ketoacidosis.

Question 18: A laboratory is validating the precision of a new assay. A control material is analyzed 20 times, yielding a mean value of 80 mg/dL and a standard deviation (SD) of 4 mg/dL. What is the coefficient of variation (CV)?

5.0% (Correct answer)
0.5%
20.0%
2.0%

Correct answer: 5.0%

The coefficient of variation (CV) is a measure of relative variability. The formula is CV (%) = (Standard Deviation / Mean) × 100. For this data: (4 mg/dL / 80 mg/dL) × 100 = 5.0%.

Question 19: Which method is considered the reference method for measuring total cholesterol?

Ultracentrifugation
Friedewald calculation
Enzymatic colorimetric method
Abell-Kendall method (Correct answer)

Correct answer: Abell-Kendall method

The Abell-Kendall method, based on the Liebermann-Burchard reaction after saponification and extraction, is the CDC-designated reference method for total cholesterol.

Question 20: What does a Southern blot technique detect?

Specific DNA sequences (Correct answer)
Specific proteins
Specific RNA sequences
Specific antibodies

Correct answer: Specific DNA sequences

Southern blotting transfers denatured DNA from a gel to a membrane, where it is hybridized with a labeled probe to detect specific DNA sequences.

Question 21: In von Willebrand disease type 1, which laboratory finding is most expected?

Normal aPTT with elevated fibrinogen
Decreased platelet count with normal bleeding time
Prolonged bleeding time with decreased vWF antigen (Correct answer)
Prolonged PT with normal aPTT

Correct answer: Prolonged bleeding time with decreased vWF antigen

Type 1 von Willebrand disease is a partial quantitative deficiency of vWF, leading to prolonged bleeding time and decreased vWF antigen levels.

Question 22: A patient with sickle cell disease has developed multiple alloantibodies after chronic transfusions. Which antigen matching strategy best prevents further alloimmunization?

Crossmatch-compatible units without additional phenotyping
Irradiated, leukoreduced random donor units
ABO and Rh(D) matching only
Extended phenotype matching for Rh and Kell antigens at minimum (Correct answer)

Correct answer: Extended phenotype matching for Rh and Kell antigens at minimum

Extended phenotype matching for at least Rh (C, E, c, e) and Kell antigens significantly reduces alloimmunization rates in chronically transfused sickle cell patients.

Question 23: Which of the following actions is MOST appropriate when a QC result violates a rejection rule before reporting patient results?

Report patient results and repeat QC later
Report only results that fall within the reference interval
Adjust the QC mean to accept the result
Hold patient results, identify the problem, and repeat QC (Correct answer)

Correct answer: Hold patient results, identify the problem, and repeat QC

Patient results must be held until the QC problem is identified and corrective action is verified by repeat QC.

Question 24: In urinalysis, the presence of waxy casts most commonly indicates what condition?

Acute pyelonephritis
Nephrotic syndrome
Urinary tract infection
Chronic renal failure (Correct answer)

Correct answer: Chronic renal failure

Waxy casts form in dilated tubules with prolonged urine stasis, indicating chronic renal failure.

Question 25: A patient on warfarin therapy has an INR of 5.8 with active bleeding. Which product provides the most rapid reversal of warfarin's anticoagulant effect?

Fresh frozen plasma (FFP)
Cryoprecipitate
Vitamin K (IV)
4-factor prothrombin complex concentrate (4F-PCC) (Correct answer)

Correct answer: 4-factor prothrombin complex concentrate (4F-PCC)

4-factor PCC (containing Factors II, VII, IX, and X) provides immediate reversal of warfarin by directly replacing all vitamin K-dependent clotting factors. It acts faster than FFP (no thawing delay, smaller volume) and far faster than IV Vitamin K, which requires hours for hepatic synthesis of new factors. Cryoprecipitate does not contain the relevant factors.

Question 26: During a pretransfusion compatibility test, a medical laboratory technician finds that the patient's ABO/Rh type is A positive, and the antibody screen is negative. The crossmatch is performed with an A positive donor unit. The immediate spin crossmatch is incompatible (4+). What is the MOST likely cause of this discrepancy?

The patient has a cold-reacting alloantibody not detected by the screen.
The donor unit is incorrectly labeled and is actually group B.
The patient has an antibody to a low-prevalence antigen present on the donor's red cells.
The patient has an A2 subtype with the presence of anti-A1. (Correct answer)

Correct answer: The patient has an A2 subtype with the presence of anti-A1.

An A2 individual can produce anti-A1, which would react with A1 cells from the donor unit, causing an incompatibility at immediate spin. The antibody screen is typically performed with O cells, which would not detect anti-A1. An incorrect donor unit label (e.g., group B) would also cause incompatibility, but the A2 with anti-A1 scenario is a classic cause for this specific set of results. An antibody to a low-prevalence antigen is possible but less common, and a cold antibody should have been detected on the screen if the appropriate cells were used.

Question 27: A patient's blood sample shows microcytic, hypochromic red blood cells with an elevated red cell distribution width (RDW). Which condition is most consistent with these findings?

Anemia of chronic disease
Iron deficiency anemia (Correct answer)
Thalassemia trait
Sideroblastic anemia

Correct answer: Iron deficiency anemia

Iron deficiency anemia classically presents with microcytic, hypochromic cells and an elevated RDW due to progressive iron depletion causing variable cell sizes.

Question 28: A gram-negative rod isolated from a urine culture grows as dry, pink colonies on MacConkey agar. The following biochemical test results are obtained: Indole: Positive Methyl Red: Positive Voges-Proskauer: Negative Citrate: Negative What is the most probable identification of this organism?

Pseudomonas aeruginosa
Escherichia coli (Correct answer)
Proteus mirabilis
Klebsiella pneumoniae

Correct answer: Escherichia coli

This classic IMViC (Indole, Methyl Red, Voges-Proskauer, Citrate) reaction pattern of ++-- is characteristic of *Escherichia coli*. The organism's ability to ferment lactose (pink colonies on MacConkey) further supports this identification.

Question 29: A laboratory records the following QC results for sodium: 139, 138, 141, 137, 140, 142, 138 mEq/L (mean=139, SD=1.7). The R-4s rule compares:

Consecutive control results from the same level to the ±2 SD range
Results from two different control levels to a single 2 SD limit
The current run mean to the cumulative mean over 30 days
The highest and lowest results within a single run to the 4 SD range (Correct answer)

Correct answer: The highest and lowest results within a single run to the 4 SD range

The R-4s rule is violated when the range between the highest and lowest QC result within one run exceeds 4 SD, indicating random error.

Question 30: Gel electrophoresis separates DNA fragments based on:

Fragment size (number of base pairs) (Correct answer)
Degree of methylation
GC content
Molecular weight and charge

Correct answer: Fragment size (number of base pairs)

In agarose gel electrophoresis, DNA fragments migrate through the gel matrix under an electric field; smaller fragments migrate faster and farther, separating fragments by size (base pairs).

Question 31: Next-generation sequencing (NGS) differs from Sanger sequencing primarily in that NGS:

Is less accurate than Sanger sequencing
Can only sequence short fragments of DNA
Requires more sample volume than Sanger
Sequences millions of DNA fragments simultaneously in a massively parallel manner (Correct answer)

Correct answer: Sequences millions of DNA fragments simultaneously in a massively parallel manner

NGS platforms sequence millions of DNA fragments simultaneously through massively parallel processing, enabling whole-genome or whole-exome analysis at far greater throughput than Sanger sequencing.

Question 32: Which fungal organism appears as large, broad-based budding yeast cells in a KOH preparation of lung tissue from a patient in the Ohio River Valley?

Cryptococcus neoformans
Histoplasma capsulatum
Coccidioides immitis
Blastomyces dermatitidis (Correct answer)

Correct answer: Blastomyces dermatitidis

Blastomyces dermatitidis produces large thick-walled yeast with characteristic broad-based buds and is endemic to the Ohio and Mississippi River valleys.

Question 33: What is the confirmatory test for syphilis after a reactive RPR screening result?

RPR titer
FTA-ABS (Correct answer)
VDRL
Dark-field microscopy

Correct answer: FTA-ABS

The FTA-ABS is a treponemal-specific confirmatory test used to verify reactive nontreponemal screening results.

Question 34: A serum protein electrophoresis shows a tall, narrow spike in the gamma region. Which laboratory finding would most support a diagnosis of multiple myeloma?

Neutrophilia with toxic granulation
Decreased ESR and normal serum calcium
Elevated serum albumin with polyclonal hypergammaglobulinemia
Bence Jones proteins in urine and rouleaux formation on peripheral smear (Correct answer)

Correct answer: Bence Jones proteins in urine and rouleaux formation on peripheral smear

Multiple myeloma is characterized by a monoclonal (M) protein spike, and malignant plasma cells often secrete free immunoglobulin light chains (Bence Jones proteins) detectable in urine. The excess immunoglobulins also cause RBCs to stack (rouleaux), seen on peripheral blood smear.

Question 35: Which electrolyte measurement is most affected by hemolysis of a blood specimen?

Sodium
Chloride
Bicarbonate
Potassium (Correct answer)

Correct answer: Potassium

Potassium is present in much higher concentrations inside red blood cells than in plasma, so hemolysis causes a significant falsely elevated potassium result.

Question 36: An MLT inoculates a urine specimen onto a culture medium that is designed to inhibit the growth of Gram-positive organisms while differentiating between bacteria that can and cannot ferment lactose. Lactose fermenters produce pink-to-red colonies on this medium. What is this type of agar called?

Blood agar
MacConkey agar (Correct answer)
Mannitol salt agar
Chocolate agar

Correct answer: MacConkey agar

MacConkey agar is both selective and differential. It contains bile salts and crystal violet to inhibit most Gram-positive bacteria, making it selective. It also contains lactose and the pH indicator neutral red, which differentiates lactose-fermenting bacteria (which turn pink/red) from non-lactose fermenters.

Question 37: In laboratory quality management, 'total allowable error' (TEa) defines:

The SD limit beyond which an instrument must be serviced
The maximum difference between two QC levels
The number of errors permitted per 1,000 patient samples
The maximum error acceptable for a test to be clinically useful (Correct answer)

Correct answer: The maximum error acceptable for a test to be clinically useful

TEa is the maximum permissible combination of imprecision and inaccuracy for a test result to remain clinically meaningful.

Question 38: Which reaction is the basis for the methodologies employed for the quantitation of bilirubin in serum/plasma samples?

Jaffe
Biuret
Diazo (Correct answer)
Rous

Correct answer: Diazo

The diazo reaction is the fundamental chemical principle employed for the quantitative measurement of bilirubin in serum or plasma samples. In this reaction, bilirubin reacts with a diazonium salt to form azobilirubin, a colored compound. The intensity of this color is then measured spectrophotometrically, allowing for accurate determination of bilirubin concentration.

Question 39: Which of the following is the correct order of draw when collecting multiple tubes via venipuncture, according to CLSI guidelines?

EDTA (lavender) → SST (gold) → Heparin (green) → Citrate (blue) → Blood culture
Heparin (green) → Citrate (blue) → Blood culture → EDTA (lavender) → SST (gold)
SST (gold) → Blood culture → Citrate (blue) → EDTA (lavender) → Heparin (green)
Blood culture → Citrate (blue) → SST (gold) → Heparin (green) → EDTA (lavender) (Correct answer)

Correct answer: Blood culture → Citrate (blue) → SST (gold) → Heparin (green) → EDTA (lavender)

CLSI order of draw is blood culture bottles first, then citrate (blue), SST (gold), heparin (green), EDTA (lavender) to prevent additive cross-contamination.

Question 40: A QC chart shows seven consecutive control values all falling on the same side of the mean. Which Westgard rule does this pattern violate?

R-4s rule
2-2s rule
1-3s rule
10x rule (Correct answer)

Correct answer: 10x rule

The 10x rule is triggered when ten consecutive control measurements fall on the same side of the mean, indicating a systematic shift or bias in the method. Seven consecutive points on one side is an early warning of the same trend, and the 10x rule specifically addresses this systematic error pattern.

Question 41: What does an elevated serum AST-to-ALT ratio greater than 2:1 typically suggest?

Obstructive jaundice
Alcoholic liver disease (Correct answer)
Viral hepatitis
Hemolytic anemia

Correct answer: Alcoholic liver disease

An AST-to-ALT ratio greater than 2:1 is a classic pattern associated with alcoholic liver disease due to alcohol-induced mitochondrial damage releasing more AST.

Question 42: Which of the following white blood cell types is the FIRST to respond to an acute bacterial infection?

Eosinophils
Monocytes
Lymphocytes
Neutrophils (Correct answer)

Correct answer: Neutrophils

Neutrophils are the primary first-responders in acute bacterial infections. They are phagocytic cells that rapidly migrate to sites of infection, and a left shift (increase in band neutrophils) is a classic laboratory finding.

Question 43: A medical laboratory technician is performing a differential on a Wright-stained peripheral blood smear. They identify red blood cell inclusions that are small, irregular, basophilic granules clustered near the periphery of the cell. A Prussian blue stain confirms the presence of iron. What are these inclusions?

Basophilic stippling
Howell-Jolly bodies
Pappenheimer bodies (Correct answer)
Cabot rings

Correct answer: Pappenheimer bodies

Pappenheimer bodies are abnormal granules of iron, visible as basophilic inclusions on a Wright stain. [22, 30] Their presence is confirmed with a special iron stain like Prussian blue. [24] Howell-Jolly bodies are DNA remnants and are typically single, round, and dense. [24, 28] Basophilic stippling consists of precipitated ribosomes and appears as fine or coarse granules distributed throughout the cell. Cabot rings are rare, thread-like inclusions thought to be remnants of the mitotic spindle.

Question 44: In a Westgard multirule QC system, a 2-2s violation occurs when which of the following is observed?

The range between two controls exceeds 4 standard deviations
Two consecutive controls exceed 2 standard deviations on the same side of the mean (Correct answer)
One control exceeds 2 standard deviations from the mean
Two consecutive controls exceed 2 standard deviations on opposite sides of the mean

Correct answer: Two consecutive controls exceed 2 standard deviations on the same side of the mean

A 2-2s violation is triggered when two consecutive control results both exceed 2 standard deviations from the mean on the same side, indicating systematic error.

Question 45: A urine dipstick shows a positive nitrite result. This finding most likely indicates the presence of:

Renal calculi
Gram-negative bacteria (Correct answer)
Fungal infection
Gram-positive cocci

Correct answer: Gram-negative bacteria

Many gram-negative bacteria (e.g., E. coli) convert dietary nitrates to nitrites via reductase enzymes. A positive nitrite result strongly suggests a urinary tract infection caused by gram-negative organisms.

Question 46: A patient types as group O with anti-A and anti-B but shows a weak forward reaction with anti-A,B reagent. The most likely explanation is:

Bombay phenotype
Cold autoantibody interference
A subgroup such as Ax (Correct answer)
Acquired B antigen

Correct answer: A subgroup such as Ax

Weak A subgroups (Ax, Aend) may not react with individual anti-A but can react with the cross-reacting anti-A,B reagent, revealing residual A antigen.

Question 47: To find comprehensive information regarding the hazards, safe handling, and emergency procedures for a new chemical reagent, an MLT should primarily consult the:

Safety Data Sheet (SDS) (Correct answer)
Instrument operation manual
Laboratory's Standard Operating Procedure (SOP)
Annual CAP inspection checklist

Correct answer: Safety Data Sheet (SDS)

The Safety Data Sheet (SDS), formerly MSDS, is a document mandated by OSHA that provides detailed information about a hazardous chemical. It includes properties, health hazards, protective measures, and safety precautions for handling, storing, and emergency response.

Question 48: A physician orders a trough level for vancomycin, a therapeutic drug. When is the appropriate time to collect the blood specimen for this test?

60 minutes after the intravenous dose is complete
Up to 30 minutes before the next scheduled dose (Correct answer)
At a random time between doses
Immediately after the intravenous dose is complete

Correct answer: Up to 30 minutes before the next scheduled dose

A trough level represents the lowest concentration of a drug in the bloodstream before the next dose is administered. To accurately measure this, the sample should be drawn immediately before (up to 30 minutes prior to) the next dose.

Question 49: Loop-mediated isothermal amplification (LAMP) differs from PCR in that LAMP:

Requires a thermal cycler with precise temperature changes
Can only detect RNA targets
Amplifies DNA at a constant temperature without thermal cycling (Correct answer)
Produces longer amplicons than PCR

Correct answer: Amplifies DNA at a constant temperature without thermal cycling

LAMP uses strand displacement DNA synthesis at a constant temperature (60-65°C) with a set of 4-6 primers, making it suitable for point-of-care testing without specialized thermocyclers.

Question 50: Which agency establishes the Clinical Laboratory Improvement Amendments (CLIA) regulations that govern laboratory testing in the United States?

CMS (Correct answer)
OSHA
FDA
CDC

Correct answer: CMS

The Centers for Medicare & Medicaid Services (CMS) is the federal agency responsible for implementing and enforcing CLIA regulations for clinical laboratories.

Question 51: Which of the following laboratory tests is most crucial for monitoring the effectiveness of warfarin (Coumadin®) therapy?

Activated Partial Thromboplastin Time (aPTT)
Thrombin Time (TT)
Fibrinogen Level
Prothrombin Time / International Normalized Ratio (PT/INR) (Correct answer)

Correct answer: Prothrombin Time / International Normalized Ratio (PT/INR)

Warfarin is a vitamin K antagonist that inhibits the synthesis of clotting factors II, VII, IX, and X. The Prothrombin Time (PT) test evaluates the extrinsic and common coagulation pathways, which include these factors. The International Normalized Ratio (INR) standardizes the PT result, making it the primary test for monitoring warfarin therapy.

Question 52: A patient presents with mucocutaneous bleeding. Laboratory findings include a normal platelet count, giant platelets on the peripheral smear, and impaired platelet aggregation with ristocetin. Aggregation with ADP, collagen, and epinephrine is normal. These findings are most consistent with which platelet disorder?

Idiopathic Thrombocytopenic Purpura (ITP)
Glanzmann Thrombasthenia
Bernard-Soulier Syndrome (Correct answer)
von Willebrand Disease

Correct answer: Bernard-Soulier Syndrome

Bernard-Soulier Syndrome is characterized by a defect in the GPIb/IX/V complex on the platelet surface, which is the receptor for von Willebrand factor. This leads to defective platelet adhesion. Key lab findings include thrombocytopenia (often mild), giant platelets, and a lack of aggregation with ristocetin, while aggregation to other agonists like ADP is normal.

Question 53: A laboratory employee accidentally splashes an unknown chemical reagent into their eyes. What is the immediate first action that should be taken?

Flush the eyes at the eyewash station with water for at least 15 minutes (Correct answer)
Notify the supervisor and wait for instructions
Consult the Safety Data Sheet to identify the chemical before acting
Apply a neutralizing solution recommended by the chemical manufacturer

Correct answer: Flush the eyes at the eyewash station with water for at least 15 minutes

Immediate, continuous flushing of the eyes with water for a minimum of 15 minutes at an eyewash station is the correct first response to a chemical eye splash. Delaying action to consult an SDS or await instructions can worsen injury.

Question 54: Which urine chemical test principle relies on the double indicator method to detect pH?

Clinitest copper reduction tablet
Reagent strip pH pad using methyl red and bromothymol blue (Correct answer)
Sulfosalicylic acid precipitation
Ictotest diazo reaction

Correct answer: Reagent strip pH pad using methyl red and bromothymol blue

The reagent strip pH pad uses the double indicator system of methyl red and bromothymol blue to cover pH ranges from 5 to 9.

Question 55: According to AABB Standards, the minimum hemoglobin content in a unit of packed red blood cells must be at least:

51 g per unit (Correct answer)
45 g per unit
60 g per unit
70 g per unit

Correct answer: 51 g per unit

AABB Standards require ≥51 g of hemoglobin per RBC unit (≥80% of units tested) to ensure adequate therapeutic content.

Question 56: A patient presents to the emergency department with chest pain. Which of the following cardiac markers is the earliest to rise following an acute myocardial infarction (AMI)?

Creatine Kinase-MB (CK-MB)
Cardiac Troponin I (cTnI)
Myoglobin (Correct answer)
Lactate Dehydrogenase (LDH)

Correct answer: Myoglobin

Myoglobin is a small protein found in heart and skeletal muscle. Due to its low molecular weight, it is released rapidly into the bloodstream following muscle injury and can be detected as early as 1-4 hours after an AMI, making it the earliest marker.

Question 57: A blood bank technologist performs a DAT on a post-transfusion sample and obtains a mixed-field reaction. What does this finding most likely indicate?

Circulating transfused donor cells are being coated with recipient antibody in vivo (Correct answer)
The patient has a positive DAT due to drug-induced antibody
The polyspecific AHG reagent is contaminated
The patient has a cold autoantibody

Correct answer: Circulating transfused donor cells are being coated with recipient antibody in vivo

A mixed-field DAT after transfusion indicates that some cells (transfused donor cells) are coated with antibody while the patient's own cells remain uncoated.

Question 58: Which storage lesion change is most significant in red blood cells stored beyond 35 days in CPDA-1?

Increased ATP levels
Decreased potassium concentration in the supernatant
Decreased 2,3-DPG levels causing increased oxygen affinity (Correct answer)
Improved red cell deformability

Correct answer: Decreased 2,3-DPG levels causing increased oxygen affinity

Stored red blood cells progressively lose 2,3-DPG, which increases hemoglobin's oxygen affinity and reduces oxygen delivery to tissues.

Question 59: A laboratory is validating a new chemistry analyzer. Which parameter assesses the agreement between the new method and the existing reference method?

Precision
Accuracy
Linearity
Method comparison (Correct answer)

Correct answer: Method comparison

Method comparison studies evaluate the agreement between a new analyzer and an established reference method by testing patient samples on both systems.

Question 60: Which type of hypersensitivity reaction is responsible for contact dermatitis caused by poison ivy?

Type III – immune complex
Type I – IgE-mediated
Type IV – delayed-type (cell-mediated) (Correct answer)
Type II – cytotoxic

Correct answer: Type IV – delayed-type (cell-mediated)

Contact dermatitis is a Type IV (delayed-type) hypersensitivity reaction mediated by sensitized T lymphocytes, not antibodies.

Question 61: A positive internal control in a PCR assay serves to:

Confirm the target sequence is absent
Indicate sample contamination
Determine the melting temperature of the amplicon
Verify that PCR inhibitors in the specimen did not prevent amplification (Correct answer)

Correct answer: Verify that PCR inhibitors in the specimen did not prevent amplification

An internal control (co-amplified with the target) confirms that the PCR reaction worked properly; if the internal control fails to amplify, it suggests inhibitors in the specimen caused a false-negative result.

Question 62: A patient's serum shows a prozone phenomenon in an RPR test. What should the laboratory do?

Repeat using undiluted serum twice
Confirm with a treponemal test immediately
Report the result as negative
Dilute the serum and repeat the test (Correct answer)

Correct answer: Dilute the serum and repeat the test

Prozone occurs with antibody excess; diluting the serum allows lattice formation and produces a visible agglutination reaction.

Question 63: When applying the albumin-adjusted calcium formula in clinical chemistry to correct total calcium for hypoalbuminemia, how much is added to the measured total calcium for each 1 g/dL that serum albumin falls below 4 g/dL?

1.2 mg/dL
2.0 mg/dL
0.4 mg/dL
0.8 mg/dL (Correct answer)

Correct answer: 0.8 mg/dL

Approximately 40–45% of serum calcium is protein-bound, primarily to albumin. The standard correction formula adds 0.8 mg/dL to total calcium for every 1 g/dL decrease in albumin below the reference value of 4 g/dL, estimating what total calcium would be under normal albumin conditions.

Question 64: A laboratory technician notices a false-negative agglutination result in a patient sample despite known antibody presence. Repeating the test after diluting the serum gives a positive result. This finding is most consistent with which phenomenon?

Postzone phenomenon
Prozone phenomenon (Correct answer)
Complement fixation inhibition
Hook effect (high-dose hook)

Correct answer: Prozone phenomenon

The prozone phenomenon occurs when excess antibody relative to antigen saturates all available antigenic sites, preventing the cross-linking (lattice formation) needed for visible agglutination. Diluting the serum reduces antibody excess and allows lattice formation, producing a positive result.

Question 65: Which technique uses labeled probes hybridized to target nucleic acid on a membrane to detect gene expression patterns?

PCR
Northern blot (Correct answer)
Western blot
Flow cytometry

Correct answer: Northern blot

Northern blotting transfers RNA to a membrane and hybridizes it with labeled probes to detect and quantify specific RNA (mRNA) sequences, providing information about gene expression levels.

Question 66: A patient with blood type AB positive requires a platelet transfusion, but only type O platelets are available. What is the primary concern with this transfusion?

There is no concern because platelets do not carry ABO antigens
The platelets will be immediately destroyed by the recipient's immune system
Rh incompatibility will trigger an acute hemolytic reaction
Anti-A and anti-B antibodies in the donor plasma may cause hemolysis (Correct answer)

Correct answer: Anti-A and anti-B antibodies in the donor plasma may cause hemolysis

Type O platelet units contain donor plasma with anti-A and anti-B antibodies that can cause hemolysis of the recipient's red blood cells.

Question 67: Which cell type is the primary precursor of platelets in the bone marrow?

Myeloblast
Promonocyte
Reticulocyte
Megakaryocyte (Correct answer)

Correct answer: Megakaryocyte

Megakaryocytes are large bone marrow cells that shed cytoplasmic fragments to produce platelets.

Question 68: What corrective action should be taken when a Levy-Jennings chart shows a sudden upward shift in control values starting after a reagent lot change?

Continue testing and monitor for further shifts
Perform a new proficiency testing event
Report all patient results since they are within reportable range
Rerun controls using the previous reagent lot to confirm the new lot is the cause (Correct answer)

Correct answer: Rerun controls using the previous reagent lot to confirm the new lot is the cause

When a shift coincides with a reagent lot change, rerunning controls with the previous lot helps confirm whether the new reagent is causing the problem.

Question 69: Which of the following is a common inhibitor of PCR found in blood specimens?

Sodium citrate
EDTA
Heparin (Correct answer)
Lithium heparin versus regular heparin (both equally inhibit)

Correct answer: Heparin

Heparin is a potent PCR inhibitor because it binds to DNA polymerase and prevents it from functioning; EDTA-anticoagulated blood is preferred for molecular testing.

Question 70: An antibody panel has been performed on a patient with a positive antibody screen. To confirm the identity of a suspected antibody, such as anti-Jka, and to ensure other clinically significant antibodies are not being missed, the technologist must follow the 'rule of three.' What does this rule require?

The patient's serum must be reactive with at least three different crossmatch-compatible units.
The patient's serum must be reactive with at least three antigen-positive cells and non-reactive with at least three antigen-negative cells. (Correct answer)
The antibody must be identified by three different technologists before reporting.
The patient's serum must be non-reactive with at least three antigen-positive cells and reactive with three antigen-negative cells.

Correct answer: The patient's serum must be reactive with at least three antigen-positive cells and non-reactive with at least three antigen-negative cells.

The 'rule of three' in antibody identification provides statistical confidence (p-value ≤ 0.05) that the identified antibody is correct and the reactivity is not due to chance. It requires demonstrating that the patient's serum reacts with at least three panel cells that are positive for the corresponding antigen and does not react with at least three panel cells that are negative for that antigen.

Question 71: Which crystal found in acidic urine appears as a hexagonal flat plate and is associated with an inherited metabolic disorder?

Amorphous urates
Cystine (Correct answer)
Uric acid
Calcium oxalate

Correct answer: Cystine

Cystine crystals appear as colorless hexagonal plates in acidic urine and indicate cystinuria, an inherited amino acid transport disorder.

Question 72: Granulocyte transfusions should be irradiated primarily to prevent:

Febrile non-hemolytic transfusion reactions
Transfusion-associated graft-versus-host disease (Correct answer)
Alloimmunization to HLA antigens
CMV transmission

Correct answer: Transfusion-associated graft-versus-host disease

Granulocyte components contain large numbers of T lymphocytes, making irradiation essential to prevent TA-GvHD.

Question 73: Which colorimetric method is the standard clinical laboratory procedure for measuring total protein in serum, based on the reaction of peptide bonds with copper ions in alkaline solution?

Bradford assay
BCA (bicinchoninic acid) assay
Lowry method
Biuret method (Correct answer)

Correct answer: Biuret method

The biuret method is the standard clinical chemistry procedure for total serum protein. Copper(II) ions in alkaline solution form a violet complex with peptide bonds (two or more), producing a color proportional to protein concentration measured at 540 nm.

Question 74: Secretory IgA differs from serum IgA primarily in that secretory IgA:

Contains a J chain and secretory component (Correct answer)
Is produced by plasma cells in bone marrow
Is a monomer
Activates complement via the classical pathway

Correct answer: Contains a J chain and secretory component

Secretory IgA is a dimer joined by a J chain and protected by a secretory component added during transcytosis across epithelial cells.

Question 75: Which electrolyte imbalance is most commonly associated with hemolyzed blood specimens?

Falsely elevated calcium
Falsely decreased chloride
Falsely elevated potassium (Correct answer)
Falsely decreased sodium

Correct answer: Falsely elevated potassium

Hemolysis releases intracellular potassium into the serum, causing a falsely elevated potassium result.

Question 76: HLA typing is most critical before which clinical procedure?

Platelet apheresis donation
Bone marrow biopsy
Autologous blood transfusion
Solid organ transplantation (Correct answer)

Correct answer: Solid organ transplantation

HLA matching between donor and recipient is essential in solid organ transplantation to minimize rejection risk.

Question 77: A new lot of QC material is being validated. The laboratory should establish the mean and SD by running the QC material at least:

3 times on consecutive days
20 times over multiple days (Correct answer)
5 times over 1 day
10 times over 2 days

Correct answer: 20 times over multiple days

At least 20 replicates run over multiple days are recommended to establish reliable QC mean and SD values.

Question 78: A patient presents with vulvovaginitis, and a culture of the vaginal discharge grows creamy, white colonies on Sabouraud dextrose agar. A wet mount prepared from a colony reveals oval-shaped budding cells and elongated structures that look like links of sausage, referred to as pseudohyphae. What is the most likely pathogen?

Aspergillus fumigatus
Cryptococcus neoformans
Candida albicans (Correct answer)
Trichomonas vaginalis

Correct answer: Candida albicans

Candida albicans is a polymorphic fungus that is a common cause of vaginitis. It is characterized by its ability to grow as budding yeast cells and to form pseudohyphae and true hyphae. The observation of both budding yeast and pseudohyphae is highly suggestive of Candida albicans. Aspergillus is a mold, Cryptococcus is an encapsulated yeast that does not typically form pseudohyphae, and Trichomonas is a protozoan parasite.

Question 79: In the uricase (enzymatic) method for measuring uric acid in clinical chemistry, what is the direct product detected to quantify uric acid concentration?

Hydrogen peroxide, which reacts with a chromogen via peroxidase to produce a colored product (Correct answer)
Ammonia produced from nitrogen-containing ring cleavage
Carbon dioxide released during uric acid oxidation
Allantoin measured directly by spectrophotometry at 293 nm

Correct answer: Hydrogen peroxide, which reacts with a chromogen via peroxidase to produce a colored product

Uricase oxidizes uric acid to allantoin and hydrogen peroxide. The H2O2 produced then reacts with a chromogenic oxygen acceptor in the presence of peroxidase (Trinder reaction) to generate a colored compound measured photometrically, providing a specific and sensitive assay.

Question 80: Which fire extinguisher class is appropriate for an electrical equipment fire in the chemistry analyzer area?

Class A
Class D
Class B
Class C (Correct answer)

Correct answer: Class C

Class C fire extinguishers are specifically designed for fires involving energized electrical equipment.

Question 81: In the coagulation cascade, which factor acts as the common pathway 'entry point' activated by both the intrinsic (contact) and extrinsic (tissue factor) pathways?

Factor XI
Factor IX
Factor X (Correct answer)
Factor VII

Correct answer: Factor X

Factor X (Stuart-Prower factor) is the junction where both pathways converge. The intrinsic pathway activates Factor X via the tenase complex (IXa + VIIIa), while the extrinsic pathway activates it via the extrinsic tenase complex (TF + VIIa). Activated Factor Xa then combines with Factor Va to form prothrombinase.

Question 82: A urine reagent strip is positive for blood, but subsequent microscopic examination reveals no red blood cells. Which of the following is the most likely cause for this discrepancy?

Presence of yeast resembling RBCs
Contamination with ascorbic acid
Presence of myoglobin (Correct answer)
High specific gravity crenating the cells

Correct answer: Presence of myoglobin

The blood pad on the reagent strip detects the peroxidase-like activity of the heme portion of hemoglobin and myoglobin. In cases of rhabdomyolysis (muscle breakdown), myoglobin is released and filtered by the kidneys, causing a positive reagent strip result for blood. However, since there are no intact red blood cells, the microscopic exam will be negative.

Question 83: A medical laboratory technician performs a Gram stain on a positive blood culture bottle. Microscopic examination reveals spherical bacteria arranged in grape-like clusters that stain purple. Which of the following organisms is most suggested by this morphology?

Neisseria meningitidis
Streptococcus pyogenes
Staphylococcus aureus (Correct answer)
Escherichia coli

Correct answer: Staphylococcus aureus

The key descriptors are "Gram-positive (purple) cocci (spherical) in grape-like clusters." This morphology is characteristic of Staphylococcus species. Streptococcus species are also Gram-positive cocci but typically form chains. Neisseria are Gram-negative diplococci, and E. coli is a Gram-negative rod.

Question 84: A neonate is found to have anti-c in maternal serum. Which Rh phenotype should be selected for exchange transfusion?

R0r (cDe/cde)
R1R1 (CDe/CDe) (Correct answer)
R2R2 (cDE/cDE)
rr (cde/cde)

Correct answer: R1R1 (CDe/CDe)

R1R1 (CDe/CDe) units are c-negative and will not be destroyed by maternal anti-c crossing the placenta.

Question 85: Which type of cast is most indicative of glomerular damage when found in a urine sediment examination?

Hyaline casts
Waxy casts
Granular casts
Red blood cell casts (Correct answer)

Correct answer: Red blood cell casts

Red blood cell casts form in the renal tubules when RBCs become trapped in a protein matrix, indicating glomerular bleeding.

Question 86: Which additive is included in CPDA-1 anticoagulant-preservative solution to extend RBC shelf life beyond CPD?

Mannitol
Adenine (Correct answer)
Phosphate buffer only
Sodium chloride

Correct answer: Adenine

Adenine in CPDA-1 supports ATP synthesis in stored RBCs, extending viability from 21 days (CPD) to 35 days.

Question 87: What autoimmune disease has elevated titers of double-stranded DNA (dsDNA) antibodies?

SLE (Correct answer)
CREST syndrome
Polymyositis
Scleroderma

Correct answer: SLE

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease characterized by the production of various autoantibodies. Elevated titers of double-stranded DNA (dsDNA) antibodies are highly specific for SLE and are considered a diagnostic criterion. These antibodies play a pathogenic role in the disease, contributing to kidney damage (lupus nephritis) and other organ manifestations.

Question 88: A Gram stain performed on a purulent aspirate from a skin abscess reveals gram-positive cocci arranged in grape-like clusters. Which of the following organisms is most likely responsible for the infection?

Streptococcus pyogenes
Enterococcus faecalis
Streptococcus pneumoniae
Staphylococcus aureus (Correct answer)

Correct answer: Staphylococcus aureus

*Staphylococcus aureus* is classically described as forming grape-like clusters and is a primary cause of skin and soft tissue infections, including abscesses. *Streptococcus* and *Enterococcus* species typically arrange themselves in pairs and chains.

Question 89: In an indirect fluorescent antibody (IFA) test, the patient's antibody is detected using:

A fluorescently labeled anti-human immunoglobulin (Correct answer)
An enzyme-conjugated antigen
A labeled antigen specific for the antibody
A radiolabeled complement component

Correct answer: A fluorescently labeled anti-human immunoglobulin

IFA uses a fluorescently labeled secondary antibody (anti-human Ig) to detect patient antibody bound to substrate antigen.

Question 90: Which immunoglobulin class is most abundant in serum and provides the majority of antibody-based immunity against invading pathogens?

IgE
IgM
IgG (Correct answer)
IgA

Correct answer: IgG

IgG is the most abundant immunoglobulin in serum, comprising approximately 75-80% of total serum immunoglobulins.

Question 91: A positive tuberculin (PPD) skin test reaction is read at 48–72 hours and is an example of which immune mechanism?

T cell–mediated delayed hypersensitivity (Correct answer)
Immune complex deposition
IgE-mediated degranulation
Complement-mediated lysis

Correct answer: T cell–mediated delayed hypersensitivity

PPD testing relies on Type IV delayed hypersensitivity; sensitized CD4+ T cells release cytokines causing induration at the injection site.

Question 92: A patient's urine specimen has a pH of 8.5 and a strong odor of ammonia. Microscopic analysis is most likely to reveal which of the following crystals?

Triple phosphate (Correct answer)
Uric acid
Calcium oxalate
Leucine

Correct answer: Triple phosphate

Triple phosphate (magnesium ammonium phosphate, or struvite) crystals classically form in alkaline urine (pH > 7.0). Their shape is often described as a 'coffin-lid'. The formation is frequently associated with urinary tract infections caused by urease-producing bacteria (e.g., Proteus species), which break down urea into ammonia, raising the urine pH.

Question 93: What corrective action may be necessary in order to issue a corrected laboratory report for an incorrectly reported culture ID and susceptibility?

Notifying the patient
Filing a Health Insurance Portability and Accountability Act of 1996 (HIPAA) report
Filing an FDA medical device report
Filing a quality assurance incident report (Correct answer)

Correct answer: Filing a quality assurance incident report

When an incorrect laboratory report, such as a culture ID and susceptibility, is issued, the primary corrective action is to file a quality assurance (QA) incident report. This formal process investigates the error, determines its root cause, and implements measures to prevent recurrence. It also ensures proper documentation and communication for issuing a corrected report to the clinician.

Question 94: What is a molecular beacon probe in real-time PCR?

A hairpin-shaped probe with a fluorophore and quencher that fluoresces when hybridized (Correct answer)
A protein probe that binds DNA
A linear probe that binds to the amplicon
A radioactively labeled DNA probe

Correct answer: A hairpin-shaped probe with a fluorophore and quencher that fluoresces when hybridized

Molecular beacons are hairpin-shaped oligonucleotides with a fluorophore at one end and a quencher at the other; when they hybridize to their target, the hairpin opens and fluorescence is emitted.

Question 95: The National Fire Protection Association (NFPA) 704 diamond provides a rapid visual representation of a chemical's hazards. What type of hazard is indicated by the blue quadrant?

Flammability
Special Hazard
Health (Correct answer)
Instability/Reactivity

Correct answer: Health

The NFPA 704 diamond is color-coded for specific hazards: the blue quadrant represents health hazards, red indicates flammability, yellow denotes instability (reactivity), and the white quadrant is used for special hazards (e.g., water-reactive, oxidizer).

Question 96: Which phenotype is known as the 'Bombay phenotype' and lacks H antigen on red cells?

O negative
Oh (hh) (Correct answer)
Le(a-b-)
A2 subgroup

Correct answer: Oh (hh)

The Bombay phenotype (Oh) lacks the H antigen due to homozygous h/h, making individuals incompatible with all ABO groups.

Question 97: For a qualitative VDRL test, inactivated serum is used in a quantity of

0.15 mL
0.05 mL (Correct answer)
0.02 mL
0.10 mL

Correct answer: 0.05 mL

For a qualitative VDRL (Venereal Disease Research Laboratory) test, a specific quantity of inactivated serum is required for accurate results. The standard volume used for this test is 0.05 mL. This precise measurement ensures the correct antigen-antibody ratio for flocculation to occur, allowing for the detection of reagin antibodies associated with syphilis.

Question 98: Cold agglutinin disease is most commonly caused by antibodies of which specificity?

Anti-P1
Anti-I (Correct answer)
Anti-M
Anti-Le(a)

Correct answer: Anti-I

Anti-I is the specificity of the monoclonal IgM cold agglutinin produced in cold agglutinin disease, reacting optimally at 0–4°C.

Question 99: To prevent alloimmunization to leukocyte antigens in chronically transfused patients, which blood product modification is most effective?

Leukoreduction (Correct answer)
Irradiation
Washing
Volume reduction

Correct answer: Leukoreduction

Leukoreduction is the process of removing white blood cells (leukocytes) from a blood component. This is the most effective method for reducing the risk of febrile non-hemolytic transfusion reactions and alloimmunization to HLA antigens, which are present on leukocytes. Irradiation prevents transfusion-associated graft-versus-host disease, while washing removes plasma proteins to prevent allergic reactions.

Question 100: When performing a urinalysis, a specimen that has been stored at room temperature for more than 2 hours is considered unsuitable primarily because:

Protein levels falsely decrease due to precipitation
Bacteria multiply and may cause false-positive nitrite results (Correct answer)
Glucose concentration increases with time
Red blood cells become more resistant to lysis

Correct answer: Bacteria multiply and may cause false-positive nitrite results

Bacterial proliferation at room temperature converts nitrates to nitrites and alters pH, glucose, and cellular elements, making the specimen unreliable.

Medical Laboratory Technician (MLT) Exam

The Medical Laboratory Technician (MLT) Exam exam validates essential knowledge and skills required for certification or licensure in this field.

100

Questions

120 min

Time Limit

60%

To Pass

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