MLT GlobeQCHP exam preparation (Qatar) – page 21
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
Serum K is 8.5 mmol/L and calcium is 0.4 mmol/L (1.6 mg/dL) in an outpatient with no symptoms. The most likely cause is:
K2EDTA adds potassium and chelates calcium, giving very high K with very low Ca, often with low Mg and ALP. This occurs with wrong order of draw or tube decanting.
A heparinised blood gas sample for ionised calcium is left open to air. The result is expected to be:
Loss of CO2 raises pH, increasing calcium binding to albumin and lowering ionised calcium. Samples should be anaerobic, and liquid heparin excess can also lower results by binding calcium.
A patient with palpitations has suppressed TSH, normal free T4 and raised free T3. This is called:
In T3 toxicosis only T3 is raised, often early in Graves disease or with a toxic nodule. Free T3 should be measured when TSH is suppressed and free T4 is normal.
Heterophile antibodies in a patient sample most commonly cause which error in two-site immunometric assays?
Heterophile and human anti-animal antibodies can link capture and detection antibodies without analyte, giving false positives. Blocking reagents, dilution non-linearity or another method help detect them.
A patient with pernicious anemia has very high serum LD with LD-1 greater than LD-2. This pattern is explained by:
Megaloblastic anemia causes ineffective erythropoiesis; destroyed red cell precursors release LD-1, giving a 'flipped' LD-1 > LD-2 pattern and very high total LD. Liver and muscle mainly release LD-5.
Compared with BNP, NT-proBNP:
Pro-BNP is split into active BNP (half-life about 20 min) and inactive NT-proBNP (half-life 1–2 h). NT-proBNP is more affected by reduced renal clearance.
A breathless patient with a BMI of 42 kg/m² has echocardiographic heart failure but a lower-than-expected NT-proBNP. The best explanation is:
Natriuretic peptide concentrations are lower in obese patients, so a 'normal' value does not fully exclude heart failure. Renal failure, not obesity, typically raises them.
An elderly man with Paget disease of bone has markedly raised ALP. Which test result best confirms that the ALP is not from the liver?
GGT is raised in hepatobiliary disease but not in bone disease, so raised ALP with normal GGT suggests a bone source. AST and LD are not specific for the liver.
Which apolipoprotein is the activator of lipoprotein lipase?
Apo C-II on chylomicrons and VLDL activates lipoprotein lipase, which releases fatty acids from triglyceride. Its deficiency causes severe chylomicronemia.
A 12-hour-old baby is visibly jaundiced. Which statement is correct?
Physiological jaundice appears after 24 hours; jaundice in the first day suggests hemolysis (for example HDFN) and needs prompt bilirubin measurement. Unconjugated bilirubin is the usual cause at this age.
Raised ALP is found together with raised 5′-nucleotidase. This combination indicates that the ALP is most likely from:
5′-nucleotidase rises in hepatobiliary disease but not in bone disease or pregnancy, so it helps confirm a liver source of ALP, similar to GGT.
An increased CSF/serum albumin quotient is mainly used to assess:
Albumin is made only in the liver, so a raised CSF/serum albumin ratio means more albumin is crossing into CSF, indicating barrier damage. Intrathecal IgG synthesis is judged by the IgG index or oligoclonal bands.
A blood sample is sent to test for cryoglobulins. How should it be handled?
Cryoglobulins precipitate in the cold, so the sample must be kept at 37 °C during clotting and separation; cooling early loses the protein in the clot. The serum is then stored at 4 °C to look for precipitation.
A raised urine ACR is found on a single sample collected after heavy exercise. Before diagnosing CKD, the correct next step is to:
Exercise, fever, infection and heart failure can raise albumin excretion temporarily. Albuminuria should be confirmed in at least 2 of 3 samples over 3 to 6 months, as CKD requires persistence over 3 months.
In the enzymatic ethanol assay, alcohol dehydrogenase converts ethanol to acetaldehyde. What is measured?
ADH oxidizes ethanol while NAD+ is reduced to NADH. The rise in absorbance at 340 nm is proportional to the ethanol concentration.
An adult with aspirin overdose typically shows which acid-base pattern early on?
Salicylate stimulates the respiratory centre (respiratory alkalosis) and also causes an anion gap metabolic acidosis. The mixed picture is typical of adult salicylate poisoning.
After complete removal of an AFP-producing tumor, AFP (half-life about 5 days) falls from 800 ng/mL to 400 ng/mL in 30 days. This most suggests:
With a half-life of about 5 days, AFP should fall by far more than half in 30 days (about 6 half-lives). A slow fall suggests continued production by residual tumor.
If two cells pass through the impedance aperture at the same time and are not corrected, the result is:
Coincident cells are read as one large pulse, so the count falls and the volume rises. Analyzers apply mathematical coincidence correction to minimise this.
A grossly lipemic sample gives Hb 16.5 g/dL (165 g/L), Hct 36% and MCHC 45.8 g/dL. The best way to obtain a correct hemoglobin is to:
Lipid turbidity falsely raises the optical hemoglobin, so MCH and MCHC are falsely high; plasma replacement removes the turbidity. Warming corrects cold agglutinins, not lipemia.
An analyzer reports RBC 1.8 × 10^12/L, Hb 11.0 g/dL (110 g/L), MCV 128 fL and MCHC 48 g/dL. The smear shows red cell clumps. The next step is to:
Cold agglutinins make red cell clumps count as single large cells, giving a low RBC, high MCV and impossible MCHC; warming disperses the clumps. Plasma replacement is the fix for lipemia, not agglutination.