MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 28
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A grossly hemolyzed sample is tested for bilirubin by a diazo (Jendrassik–Grof) method. The expected effect is:
Hemoglobin reacts with the diazonium salt and interferes with azobilirubin formation, giving negative bias in diazo methods. Hemolyzed samples should be recollected.
A pregnant woman at 32 weeks has severe itching of the palms and soles without a rash; ALT is mildly raised. Which test best supports the diagnosis?
Intrahepatic cholestasis of pregnancy is diagnosed by raised serum bile acids (typically 10 µmol/L or more); high values increase fetal risk. Itching may appear before other liver tests change.
A man with ulcerative colitis has raised ALP and GGT with mildly raised ALT. Cholangiography shows multiple strictures giving a 'beaded' bile duct appearance. The most likely diagnosis is:
Primary sclerosing cholangitis causes fibrosing strictures of intra- and extrahepatic ducts and is strongly linked with inflammatory bowel disease, especially ulcerative colitis.
Total protein is 7.5 g/dL (75 g/L) and albumin is 3.0 g/dL (30 g/L). What is the albumin/globulin (A/G) ratio?
Globulin = 7.5 − 3.0 = 4.5 g/dL, so A/G = 3.0 ÷ 4.5 = 0.67. A reversed ratio (below 1) is seen with low albumin and/or high globulins, as in cirrhosis or myeloma.
A 60-year-old has an IgG-kappa M-protein of 1.2 g/dL (12 g/L), 5% clonal marrow plasma cells, and no hypercalcemia, renal damage, anemia or bone lesions. By IMWG criteria this is:
MGUS requires M-protein below 3 g/dL, fewer than 10% clonal plasma cells and no myeloma-defining events. Smoldering myeloma has M-protein ≥3 g/dL or 10–60% plasma cells.
Which marker is most useful for distinguishing bacterial from viral lower respiratory tract infection and for guiding when to stop antibiotics?
Procalcitonin rises strongly in bacterial infection and is suppressed by interferon-γ in viral infection. A falling level supports stopping antibiotics. ESR and ferritin are non-specific.
A BUN result is 28 mg/dL. What is the equivalent urea concentration in SI units (mmol/L)?
BUN (mg/dL) × 0.357 = urea (mmol/L); 28 × 0.357 = 10.0 mmol/L. Multiplying by 2.14 instead converts BUN to urea in mg/dL, not mmol/L.
Why does creatinine clearance tend to overestimate the true glomerular filtration rate?
Besides glomerular filtration, some creatinine is secreted by proximal tubules, so more appears in urine than is filtered. Reabsorption would cause underestimation, which is the problem with urea, not creatinine.
An ICU patient's serum creatinine rises daily: 90, 150, then 230 µmol/L. Why should an eGFR from creatinine not be relied on at this time?
eGFR equations assume stable creatinine production and excretion. In AKI, creatinine is still rising toward a new level, so eGFR overestimates true GFR.
A 500 mg IV dose of a drug is given. Its volume of distribution is 50 L. Assuming instant distribution, what is the expected initial plasma concentration?
Concentration = dose ÷ volume of distribution = 500 mg ÷ 50 L = 10 mg/L. Dividing 50 by 500 or mixing units gives the wrong options.
A fire victim has severe lactic acidosis and high venous oxygen saturation despite normal carboxyhemoglobin. Which poison is most likely?
Cyanide blocks cytochrome c oxidase, so cells cannot use oxygen; venous blood stays highly oxygenated and anaerobic metabolism produces lactate. Burning plastics can release cyanide.
Why is red cell folate a better indicator of long-term folate status than serum folate?
Folate enters red cells only during erythropoiesis, so RBC folate reflects the previous 2–3 months. Serum folate changes quickly with recent diet. B12 deficiency can actually lower RBC folate.
A blood ethanol result is 80 mg/dL. Given ethanol molecular weight is 46, what is the result in mmol/L?
80 mg/dL = 800 mg/L; 800 ÷ 46 = 17.4 mmol/L. Forgetting to convert dL to L gives 1.7 mmol/L.
Which condition is most likely to cause a marked but temporary rise in serum PSA?
Inflammation disrupts prostate tissue so more PSA leaks into blood; PSA should be re-tested after the infection has settled. 5-alpha-reductase inhibitors lower PSA.
A woman in the third trimester of pregnancy has normal iron stores. Which iron study result is expected to be increased because of pregnancy itself?
Estrogen increases hepatic transferrin synthesis, so TIBC rises in pregnancy and with oral contraceptives, even without iron deficiency. Ferritin tends to fall during pregnancy.
In analyzers that use a peroxidase-staining channel for the WBC differential, which cell type is peroxidase-negative?
Neutrophils and eosinophils stain strongly and monocytes weakly for peroxidase, while lymphocytes (and basophils) are negative. Cells are sorted by peroxidase absorbance and size.
A citrate tube drawn after an EDTA tube gives prolonged PT and aPTT in a patient with previously normal results. The most likely reason is:
EDTA carryover binds calcium, which added calcium cannot fully correct, giving falsely prolonged clotting times. The citrate tube should be drawn before EDTA, heparin and serum tubes with additives.
In a patient with a normal fibrinogen antigen but low Clauss (functional) fibrinogen and prolonged thrombin time, the most likely diagnosis is:
A functional-to-antigen discrepancy indicates an abnormal fibrinogen molecule. In hypofibrinogenemia both activity and antigen are proportionally low; factor XIII deficiency does not prolong clotting times.
A patient with HIT is treated with intravenous argatroban. Which test is commonly used to adjust the dose?
Argatroban, a direct thrombin inhibitor, is usually monitored by aPTT (target about 1.5–3 times baseline). It also raises the INR, which matters when switching to warfarin.
A woman suspected of vWD is tested during late pregnancy and has normal VWF levels. Why should results be interpreted cautiously?
VWF is an acute-phase reactant that rises with pregnancy, estrogen, exercise and inflammation, which can hide mild type 1 vWD. Testing may need to be repeated in a baseline state.