MLT GlobeDOH exam preparation (Abu Dhabi) – page 34
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
A pregnant woman at 26 weeks has a 75 g OGTT: fasting 95 mg/dL, 1 h 170 mg/dL, 2 h 140 mg/dL. Using the one-step (IADPSG) criteria, the result is:
One-step thresholds are fasting ≥92, 1 h ≥180 and 2 h ≥153 mg/dL; any single value met is diagnostic. Needing two abnormal values applies to the two-step (Carpenter–Coustan) 100 g test.
An infant has fasting hypoglycemia, lactic acidosis, hyperuricemia, hypertriglyceridemia and a large liver. No rise in glucose follows glucagon. Which enzyme is most likely deficient?
Glucose-6-phosphatase deficiency (von Gierke, GSD type I) blocks glucose release from liver glycogen and gluconeogenesis, causing this pattern. Muscle phosphorylase deficiency (McArdle) affects muscle, not fasting glucose.
Which additives are needed in lipase reagents so that the assay is specific and fully active for pancreatic lipase?
Pancreatic lipase needs colipase and bile salts to act at the oil–water interface; bile salts also inhibit other esterases. P5P is a cofactor for aminotransferases.
A patient has prolonged apnea after succinylcholine. Serum cholinesterase is low and the dibucaine number is 20%. This suggests:
Dibucaine inhibits normal pseudocholinesterase by about 80%; a dibucaine number near 20% indicates the homozygous atypical variant, which cannot break down succinylcholine efficiently.
CSF IgG 9 mg/dL, serum IgG 1000 mg/dL, CSF albumin 20 mg/dL, serum albumin 4000 mg/dL. What is the IgG index and its meaning (reference ≤0.7)?
IgG index = (CSF IgG/serum IgG) ÷ (CSF albumin/serum albumin) = 0.009 ÷ 0.005 = 1.8. A value above about 0.7 suggests IgG production inside the CNS.
FLAER, a reagent used in flow cytometric testing for PNH on white cells, binds directly to:
FLAER is a fluorescent inactive aerolysin that binds the GPI anchor, so GPI-deficient granulocytes and monocytes show no staining. Anti-CD59 antibodies, not FLAER, are used to detect GPI-deficient red cells.
On cation-exchange HPLC, a patient shows 28% hemoglobin eluting in the HbA2 window, with mild microcytosis. The most likely explanation is:
HbE co-elutes with HbA2 on most HPLC systems; values around 25–30% indicate HbE trait. In beta-thalassemia trait HbA2 is only mildly raised, usually 3.5–7%.
A patient with Clostridium perfringens sepsis develops sudden, massive intravascular hemolysis with many spherocytes. The main mechanism is:
The C. perfringens alpha-toxin is a phospholipase (lecithinase) that digests membrane lipids, forming spherocytes and causing rapid lysis. The DAT is negative, so an IgG autoantibody is not the cause.
A child with short stature, abnormal thumbs and progressive pancytopenia is investigated. Which test confirms the most likely diagnosis?
Fanconi anemia is an inherited DNA-repair defect causing marrow failure and skeletal abnormalities. Its lymphocytes show greatly increased chromosome breakage when exposed to DNA cross-linking agents.
A family has mild hemolysis, raised MCHC and red cells in which hemoglobin appears pushed to one side, with a clear area at the other. Osmotic fragility is decreased. This is most consistent with:
Xerocytes are dehydrated cells, often due to PIEZO1 mutations, with raised MCHC and decreased osmotic fragility. Hereditary spherocytosis also raises MCHC but shows increased, not decreased, osmotic fragility.
In a patient with a plasma cell clone but no CRAB features, which finding alone is a myeloma-defining event?
IMWG biomarkers (SLiM): >=60% clonal marrow plasma cells, involved/uninvolved FLC ratio >=100 (involved FLC >=100 mg/L), or >1 focal lesion on MRI. 15% plasma cells or serum M-protein >=30 g/L define smoldering myeloma, and a urine M-protein of 300 mg/24 h meets neither smoldering (>=500 mg/24 h) nor myeloma criteria.
Th17 cells mainly protect against extracellular bacteria and fungi by producing IL-17, which recruits:
IL-17 induces chemokines that recruit neutrophils to mucosal and skin sites. Th2 cells, not Th17, drive eosinophil responses through IL-5.
A WBC count uses a 1:20 dilution. A total of 100 cells are counted in the four large corner squares (each 1 mm², depth 0.1 mm). The WBC count is:
Volume counted = 4 × 1 × 0.1 = 0.4 µL. Cells/µL = (100 × 20)/0.4 = 5000/µL = 5.0 × 10⁹/L.
A screening test with fixed sensitivity and specificity is moved from a high-prevalence clinic to the general population with low disease prevalence. What happens?
Predictive values depend on prevalence. When prevalence falls, more positives are false positives, so PPV drops, while NPV rises. Sensitivity and specificity are properties of the test itself.
Which method validation experiment is designed to estimate proportional systematic error?
In a recovery study, known amounts of analyte are added to patient samples; incomplete recovery that grows with concentration shows proportional error. Interference studies estimate constant systematic error.
Candida auris differs from Candida albicans in that C. auris typically:
C. auris grows well at 40–42 °C, does not produce germ tubes, and rarely forms hyphae or chlamydospores. Chlamydospore production on cornmeal agar is characteristic of C. albicans.
A dermatophyte isolate produces teardrop microconidia along the hyphae, a wine-red colony reverse on potato dextrose agar, and is urease negative. The most likely species is:
T. rubrum typically gives a red reverse on potato dextrose agar, teardrop microconidia and a negative urease at 7 days. T. interdigitale (mentagrophytes complex) is usually urease positive within a few days.
A black, yeast-like colony that later becomes fuzzy shows annellides producing clusters of oval conidia at their tips. This dematiaceous organism is most likely:
Exophiala (black yeast) begins yeast-like and forms tapered annellides with conidia collecting at the tip. Alternaria is a rapidly growing woolly mold with large muriform conidia.
In a patient with Plasmodium falciparum infection, finding mature schizonts in the peripheral blood is significant because it usually indicates:
Mature P. falciparum stages normally sequester in deep capillaries, so peripheral schizonts suggest heavy infection and a worse prognosis.
A malaria rapid test based on HRP2 is negative, but films show P. falciparum. A known cause of this false-negative result is:
Some P. falciparum strains lack the hrp2/hrp3 genes and produce no HRP2 antigen, so HRP2-based RDTs miss them. Very high parasitemia (prozone) can also cause false negatives.