MLS (ASCP) Practice Questions (2026) — Free Sample Questions with Answers

Answer: D

Transfusion-associated circulatory overload: TACO usually causes hypertension, jugular venous distention and a raised BNP.

Anaphylaxis from anti-IgA: Anaphylaxis causes bronchospasm, urticaria and hypotension without fever or new lung infiltrates.

Febrile nonhemolytic transfusion reaction: FNHTR causes fever and chills without hypoxemia or infiltrates.

Transfusion-related acute lung injury: Correct. Noncardiogenic pulmonary edema within 6 hours, with hypotension, fever and a normal BNP, fits TRALI. Donor anti-HLA or anti-HNA from a multiparous woman is the usual cause.

TRALI: hypoxemia and bilateral infiltrates within 6 hours, normal BNP, often from donor leukocyte antibodies; TACO: volume overload with a raised BNP.

Answer: A

Anti-Jkᵃ: Correct. Every Jk(a+) cell reacts and every Jk(a−) cell is negative. Reactions are 3+ with homozygous Jk(a+b−) cells 1 and 4 and 1+ with heterozygous cells, the dosage typical of Kidd antibodies.

Anti-Jkᵇ: Jk(b+) cells 2, 5 and 7 are nonreactive.

Anti-S: Homozygous S+s− cell 7 is negative, and S-negative cell 3 reacts.

Anti-Fyᵃ: Homozygous Fy(a+b−) cell 5 is nonreactive.

Kidd antibodies react at AHG, show dosage and cause delayed hemolytic reactions; give Jk(a−), AHG-crossmatch-compatible units.

Answer: B

1. Fetal bleed (mL whole blood) = % fetal cells × 50 = 0.8 × 50 = 40 mL.
2. Vials = 40 ÷ 30 mL per vial = 1.33.
3. Decimal below 0.5: round down to 1; then add 1 vial.
4. Give 2 vials of 300-µg RhIG.

1 vial: This omits the extra vial that is always added to cover error in the acid-elution estimate.

2 vials: Correct. The fetal bleed is 0.8 × 50 = 40 mL of whole blood; 40 ÷ 30 = 1.33, rounded down to 1, plus 1 extra vial = 2.

3 vials: This rounds 1.33 up to 2 before adding the extra vial; a decimal below 0.5 is rounded down.

4 vials: This divides by 15 mL (the packed RBC equivalent) instead of 30 mL of whole blood per vial.

One 300-µg vial covers 30 mL of fetal whole blood. Round a decimal below 0.5 down and 0.5 or more up, then add 1 vial.

Answer: C

Graves disease: The pattern matches Graves disease on paper, but the patient has no signs of hyperthyroidism and is taking high-dose biotin, which explains every result.

Heterophile antibody interference: Heterophile antibodies usually bridge the capture and detection antibodies, falsely raising sandwich results such as TSH.

Biotin interference with the immunoassays: Correct. Excess biotin blocks streptavidin binding, falsely lowering sandwich results (TSH) and falsely raising competitive results (free T4, free T3, TSH receptor antibody). The pattern mimics Graves disease in a patient without symptoms.

High-dose hook effect in the TSH assay: A hook effect needs an extremely high analyte level and would not explain the high competitive-assay results.

Biotin: sandwich assays falsely low, competitive assays falsely high; ask about supplements and retest after biotin is withheld.

Answer: B

1. Calculated osmolality = 2 × Na + glucose/18 + BUN/2.8.
2. = 280 + 5 + 5 = 290 mOsm/kg.
3. Osmolal gap = measured − calculated = 330 − 290 = 40 mOsm/kg.
4. A gap above about 10 suggests unmeasured osmoles such as ethanol, methanol or ethylene glycol.

17 mOsm/kg: This swaps the divisors, dividing glucose by 2.8 and BUN by 18.

40 mOsm/kg: Correct. Calculated osmolality = 2(140) + 90/18 + 14/2.8 = 290; gap = 330 − 290 = 40 mOsm/kg.

45 mOsm/kg: This leaves BUN out of the calculated osmolality.

180 mOsm/kg: This forgets to double the sodium.

Osmolal gap = measured − (2Na + glucose/18 + BUN/2.8); a large gap with a high anion gap acidosis suggests methanol or ethylene glycol.

Answer: C

In vitro hemolysis of the specimen: Hemolysis raises potassium, but the hemolysis index is negative, and it would not lower calcium.

True hyperkalemia from renal failure: The creatinine and ECG are normal, and renal failure does not drop calcium to 4.1 mg/dL.

Contamination of the serum with K2EDTA: Correct. K2EDTA adds potassium and chelates calcium and magnesium (ALP needs Mg and Zn, so it falls). Very high K with very low Ca, no hemolysis and a well patient points to EDTA carryover or a wrong tube.

Prolonged tourniquet time with fist pumping: Fist pumping raises potassium modestly but does not lower calcium or ALP.

High K plus very low Ca (and low ALP or Mg) in a well patient means EDTA contamination; recollect in the correct order of draw.

Answer: D

Lupus anticoagulant: A lupus anticoagulant usually fails to correct on immediate mixing and causes thrombosis rather than bleeding.

Congenital hemophilia A: A factor deficiency corrects in both the immediate and the incubated mix.

Heparin in the specimen: Heparin prolongs the immediate mix as well as the incubated mix and prolongs the thrombin time.

Acquired factor VIII inhibitor: Correct. The mix corrects at first but prolongs after incubation while the control stays normal. That time- and temperature-dependent pattern is typical of an autoantibody against factor VIII, and it fits new bleeding in an older adult.

Correction on immediate mix but prolongation after incubation = time-dependent inhibitor, typically against factor VIII.

Answer: D

1. Cells counted = 52 + 48 + 55 + 45 = 200.
2. Volume counted = 4 mm² × 0.1 mm = 0.4 mm³ (µL).
3. Cells/µL = cells × dilution ÷ volume = 200 × 20 ÷ 0.4 = 10,000/µL.
4. WBC = 10.0 ×10³/µL, within the reference range.

0.5 ×10³/µL: This leaves out the 1:20 dilution factor.

1.0 ×10³/µL: This leaves out the 0.1-mm depth, so it uses area instead of volume.

4.4 ×10³/µL: This divides by all 9 large squares instead of the 4 counted.

10.0 ×10³/µL: Correct. 200 cells × 20 ÷ (4 mm² × 0.1 mm) = 10,000/µL = 10.0 ×10³/µL.

Hemocytometer: cells/µL = cells counted × dilution ÷ (area counted in mm² × 0.1 mm depth).

Answer: A

t(15;17)(q24;q21) PML::RARA: Correct. Hypergranular abnormal promyelocytes with bundled rod-shaped inclusions and DIC define acute promyelocytic leukemia, caused by the PML::RARA fusion. Recognizing it quickly matters because it is treated with all-trans retinoic acid.

t(8;21)(q22;q22.1) RUNX1::RUNX1T1: This AML shows myeloblasts with maturation and single slender inclusions, without hypergranular promyelocytes or typical DIC.

inv(16)(p13.1q22) CBFB::MYH11: This is associated with myelomonocytic leukemia with abnormal eosinophils.

t(9;22)(q34.1;q11.2) BCR::ABL1: BCR::ABL1 defines CML (and some ALL), not a promyelocytic leukemia.

Abnormal hypergranular promyelocytes, bundled rod-shaped inclusions and DIC: APL with t(15;17) PML::RARA.

Answer: D

False-positive treponemal immunoassay; no further action: A false-positive screen is suggested only when the second treponemal test is nonreactive; here TP-PA is reactive.

Biological false-positive reaction: Biological false positives apply to nontreponemal tests such as the RPR, which is nonreactive here.

Active secondary syphilis: Secondary syphilis almost always gives a reactive RPR, usually at a high titer.

Past or present syphilis; review treatment history and stage: Correct. Two reactive treponemal tests with a nonreactive RPR indicate past treated, late latent or very early infection; without documented treatment the patient needs clinical evaluation and usually treatment.

Reverse algorithm: EIA+/RPR− goes to a second treponemal test; if it is reactive, the patient has past or present syphilis.

Answer: D

Entamoeba coli: E. coli cysts are larger, have up to eight nuclei with eccentric karyosomes and irregular chromatin, and their bars have splintered ends.

Giardia duodenalis: Giardia cysts are oval with four nuclei, axonemes and median bodies, not spherical with peripheral chromatin.

Endolimax nana: E. nana cysts are small with four large, blot-like karyosomes and no peripheral chromatin.

Entamoeba histolytica/dispar: Correct. Spherical cysts with up to four nuclei, central karyosomes, even peripheral chromatin and bars with rounded ends fit E. histolytica/dispar, reported together because they look alike.

Count nuclei and look at the karyosome: central and even (E. histolytica/dispar) versus eccentric and coarse (E. coli).

Answer: C

Plasmid-mediated AmpC beta-lactamase: AmpC enzymes are not inhibited by clavulanate and usually make the isolate cefoxitin resistant.

KPC-type carbapenemase: A carbapenemase would raise the meropenem MIC; meropenem is susceptible here.

Extended-spectrum beta-lactamase: Correct. Clavulanate lowers both cephalosporin MICs by far more than three doubling dilutions (32 to 0.5; 64 to 0.25), the phenotypic confirmation of an ESBL, with cefoxitin and meropenem unaffected.

Loss of an outer-membrane porin: Porin loss raises MICs but is not reversed by a beta-lactamase inhibitor.

ESBL confirmation: a decrease of at least three twofold dilutions in the cephalosporin MIC when clavulanate is added.

Answer: B

1. Formula: CFU/mL = colonies counted × (1 ÷ loop volume in mL).
2. Substitution: 85 × (1 ÷ 0.01 mL) = 85 × 100.
3. Result: 8,500 = 8.5 × 10³ CFU/mL.
4. Interpretation: a single uropathogen with positive leukocyte esterase, nitrite and pyuria in a symptomatic woman supports infection; identify it and test susceptibility per laboratory policy.

8.5 × 10² CFU/mL: Multiplies by 10, as if the loop delivered 0.1 mL.

8.5 × 10³ CFU/mL: Correct. A 0.01-mL loop has a factor of 100: 85 × 100 = 8,500 CFU/mL.

8.5 × 10⁴ CFU/mL: Uses the factor of 1,000 that belongs to a 0.001-mL loop.

8.5 × 10⁵ CFU/mL: Multiplies by 10,000, a factor no standard loop uses.

The loop factor is the reciprocal of the loop volume: ×1,000 for a 0.001-mL loop and ×100 for a 0.01-mL loop.

Answer: B

1. Formula: PPV = TP ÷ (TP + FP) × 100.
2. Substitution: TP = 90, FP = 30; PPV = 90 ÷ 120 × 100.
3. Result: PPV = 75.0%.
4. Interpretation: one in four positive rapid results is a false positive at this prevalence (10%); sensitivity is 90.0%, specificity 96.7%, NPV 98.9%.

25.0%: Divides false positives by all positives (30 ÷ 120), the complement of the PPV.

75.0%: Correct. PPV = true positives ÷ all test positives = 90 ÷ 120 = 75.0%.

90.0%: This is sensitivity (90 ÷ 100), which uses the culture-positive column, not the test-positive row.

96.7%: This is specificity (870 ÷ 900).

Sensitivity and specificity read down the disease columns; predictive values read across the test rows.

Answer: C

1-2s warning only; accept run 12 and report patients: A 1-2s point triggers inspection with the other rules; two consecutive points beyond +2 SD break a rejection rule.

1-3s violation indicating random error: No point exceeds +3 SD (265 mg/dL); the highest is 262 mg/dL.

2-2s violation indicating systematic error; reject and troubleshoot: Correct. Runs 11 and 12 (261.5 and 262 mg/dL) both exceed +2 SD (260 mg/dL) on the same side, a 2-2s violation that signals systematic error, so patient results are held while the cause is found.

R-4s violation indicating random error: R-4s needs one control above +2 SD and another below −2 SD in the same run; both points here are high.

Two consecutive results beyond the same 2 SD limit (2-2s) mean systematic error: reject the run and troubleshoot before reporting.