MLT GlobeMOH exam preparation (UAE) – page 25
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A patient with severe hyperlipidemia has sodium 128 mmol/L by indirect ISE and 139 mmol/L by direct ISE. The discrepancy is due to:
Indirect ISE dilutes the sample and assumes normal plasma water; excess lipid or protein reduces water fraction, giving pseudohyponatremia. Direct ISE measures activity in plasma water and is unaffected.
A patient has glucose 30 mmol/L (540 mg/dL), urea 5 mmol/L (BUN 14 mg/dL) and Na 135 mmol/L. What is the calculated osmolality using 2Na + glucose + urea (mmol/L)?
2 × 135 + 30 + 5 = 305 mmol/kg. In conventional units, 2Na + glucose/18 + BUN/2.8 gives about 305 mOsm/kg as well.
Hypomagnesemia most commonly contributes to which other electrolyte problem that fails to correct with replacement alone?
Magnesium deficiency increases renal potassium loss, so hypokalemia is resistant until magnesium is corrected. It also impairs PTH secretion, causing hypocalcemia.
An ALT result of 60 U/L must be reported in SI units. What is the result in µkat/L? (1 U = 16.67 nkat)
60 U/L × 16.67 nkat/U = 1000 nkat/L = 1.0 µkat/L. Multiplying by 0.06 confuses minutes and seconds.
A laboratory changes its enzyme assay temperature from 30 °C to 37 °C without changing reference intervals. What is the likely effect?
Within the physiological range, enzyme reaction rates rise with temperature (roughly doubling per 10 °C), so activity results rise. Reference intervals must match the assay temperature; IFCC methods use 37 °C.
An ALP result is almost undetectable in a patient with no clinical signs. The sample was collected in a lavender-top tube. The best explanation is:
ALP is a metalloenzyme that requires Zn2+ and Mg2+; EDTA removes them and inactivates the enzyme. Serum or heparinized plasma must be used.
Phototherapy lowers neonatal bilirubin mainly by:
Blue-green light converts bilirubin in the skin into photoisomers, including lumirubin, which can be excreted in bile and urine without conjugation.
A 50-year-old with acute bacterial pneumonia has serum electrophoresis done on day 3. Which pattern is expected?
The acute-phase response raises alpha-1 antitrypsin (alpha-1) and haptoglobin (alpha-2), while albumin, a negative acute-phase protein, falls. A narrow gamma spike suggests a monoclonal protein.
Paired CSF and serum samples are run on isoelectric focusing. Several IgG bands appear in CSF that are absent from serum. This finding indicates:
Oligoclonal bands present in CSF but not serum show IgG made inside the CNS, supporting multiple sclerosis. Identical bands in both fluids would reflect passive transfer from blood.
Which substance is a well-known positive interferent in the alkaline picrate (Jaffe) creatinine method?
Ketoacids such as acetoacetate form a coloured product with alkaline picrate and falsely raise Jaffe creatinine, e.g. in diabetic ketoacidosis. Bilirubin tends to cause negative, not positive, interference.
The preferred test to confirm lead exposure in a child is:
Lead is carried mainly in red cells, so whole blood lead is the standard test. Capillary screening results that are raised should be confirmed on a venous whole blood sample.
A patient pulled from a house fire has a normal pulse oximetry reading but headache and confusion. Which test is needed?
Standard pulse oximeters read carboxyhemoglobin as oxyhemoglobin and give falsely normal values. Co-oximetry measures COHb directly at several wavelengths.
A man has total PSA of 6 ng/mL (6 µg/L). A LOW percentage of free PSA suggests:
In prostate cancer, more PSA circulates bound to antiproteases, so the free fraction is lower. A high percent free PSA favours benign enlargement.
A patient with active infection has serum ferritin of 80 ng/mL (80 µg/L), low serum iron and absent marrow iron stores. Ferritin is misleading because it:
Inflammation raises ferritin independent of iron stores, so a 'normal' value can hide iron deficiency. Higher cut-offs or other markers are used in inflammation.
The immature reticulocyte fraction (IRF) is most useful as:
The IRF reflects the most RNA-rich reticulocytes and rises within days of marrow recovery, often before the neutrophil count. It does not measure iron stores; CHr or Ret-He is used for iron status.
In a manual reticulocyte count with new methylene blue, which inclusion may be wrongly counted as reticulum and falsely raise the result?
Heinz bodies, Howell-Jolly bodies and Pappenheimer bodies take up supravital dye and may be mistaken for reticulum; Heinz bodies appear as pale blue-green round bodies at the edge. Target cells and echinocytes are shape changes and do not stain.
An EDTA sample kept at room temperature for 36 hours before analysis is most likely to show:
With storage, red cells swell, increasing MCV and Hct and lowering MCHC. Hemoglobin is stable, and platelet counts tend to fall, not rise.
A 20-year-old with atypical pneumonia develops hemolysis. The DAT is positive with anti-C3 only and a cold autoantibody is present. Its specificity is most likely:
Mycoplasma pneumoniae infection often triggers polyclonal IgM anti-I cold agglutinins. Anti-i is linked with infectious mononucleosis, not Mycoplasma.
Which drug classically induces a true red cell autoantibody that is serologically identical to warm AIHA?
Methyldopa induces IgG autoantibodies, often with Rh specificity, that react with untreated red cells even without the drug. Penicillin causes hemolysis by the drug-adsorption mechanism, needing drug-coated cells to show reactivity.
Why does the PT rise within the first 1–2 days of starting warfarin, before full anticoagulation?
Factor VII's half-life is about 6 hours, so it falls first and prolongs the PT. Full antithrombotic effect needs prothrombin (half-life ~60 h) to fall.