MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 51
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
After surgical relief of a bile duct obstruction, a patient's serum direct bilirubin stays raised for weeks despite normal bile flow. The best explanation is:
Delta bilirubin is conjugated bilirubin covalently linked to albumin, so it has albumin's long half-life (about 2–3 weeks) and is not excreted in urine. It reacts in the direct bilirubin assay.
Which inherited condition causes mild conjugated hyperbilirubinemia with a normal-looking liver on biopsy (no pigment)?
Rotor syndrome gives benign conjugated hyperbilirubinemia without hepatic pigment. Gilbert and Crigler–Najjar are unconjugated disorders.
A 3-day-old boy has lethargy and ammonia above 300 µmol/L (510 µg/dL), low plasma citrulline and high urine orotic acid. The most likely disorder is:
OTC deficiency blocks carbamoyl phosphate use, which spills into pyrimidine synthesis and raises orotic acid; citrulline is low. CPS deficiency also has low citrulline but low or normal orotic acid.
Calculate the FIB-4 index: age 50 years, AST 40 U/L, ALT 25 U/L, platelets 200 × 10⁹/L. [FIB-4 = (age × AST) ÷ (platelets × √ALT)]
(50 × 40) ÷ (200 × √25) = 2000 ÷ (200 × 5) = 2000 ÷ 1000 = 2.0. Forgetting the square root of ALT gives 0.4, not 2.0.
Capillary zone electrophoresis shows a small new peak in the beta region. Immunofixation is negative. The patient had a contrast CT scan the previous day. Most likely cause?
Capillary electrophoresis detects proteins by UV absorbance near 200–214 nm; radiocontrast agents absorb at these wavelengths and create artifactual peaks. A negative immunofixation argues against a monoclonal protein.
A 24-hour urine volume is 1440 mL, urine creatinine 8.0 mmol/L and serum creatinine 100 µmol/L. What is the creatinine clearance?
Clearance = (U × V) / P. Urine flow = 1440/1440 = 1.0 mL/min; U = 8000 µmol/L; P = 100 µmol/L. So (8000 × 1.0)/100 = 80 mL/min. Forgetting to convert mmol to µmol gives a wrong answer.
Rasburicase therapy can cause falsely low uric acid results if the blood sample is:
Rasburicase is a recombinant uricase that continues to degrade uric acid in the tube. Samples should be collected into pre-chilled tubes, kept on ice and analysed promptly.
To assess chronic arsenic exposure over several months, which specimen is most useful?
Arsenic binds keratin in hair and nails, recording exposure over months. Blood arsenic clears quickly; urine reflects recent exposure.
A man with a testicular tumor diagnosed as pure seminoma on biopsy has a clearly raised serum AFP. This suggests:
Pure seminoma does not produce AFP (it may produce some hCG). A raised AFP points to a nonseminomatous germ cell element, which changes treatment.
A woman with suspected molar pregnancy has an hCG result much lower than expected. After a 1:100 dilution the result is very high. This is due to:
In one-step sandwich assays, huge antigen excess saturates both antibodies and gives a falsely low signal. Dilution brings the level into range and reveals the true high value.
In common colorimetric methods for serum iron (e.g. ferrozine), which step comes before color formation?
Acid releases Fe3+ from transferrin, a reducing agent converts it to Fe2+, and Fe2+ then forms a colored complex with the chromogen. Chromogens like ferrozine react with ferrous, not ferric, iron.
A sample from a patient with a cryoglobulin shows falsely raised WBC and platelet counts, and precipitate on the smear. The best corrective action is to:
Cryoglobulins precipitate at room temperature and the particles are counted as cells; warming dissolves them. Refrigeration increases the precipitation.
In analyzers using VCS technology, the radiofrequency (conductivity) measurement mainly gives information about a white cell's:
Low-frequency direct current measures volume, while high-frequency current passes through the membrane and reflects internal contents such as nucleus size and density. Peroxidase activity is measured by cytochemical methods, not conductivity.
A cold autoantibody causing hemolysis in a patient with infectious mononucleosis most often has which specificity?
EBV infection is associated with transient cold agglutinins of anti-i specificity, which react best with cord cells. Anti-I is the typical specificity after Mycoplasma infection.
A patient's hematocrit is 65%. Using the CLSI formula, how much 3.2% citrate is needed for 4.5 mL of whole blood?
C (mL) = 1.85 × 10^-3 × (100 − Hct) × blood volume = 0.00185 × 35 × 4.5 ≈ 0.29 mL. Using the standard 0.5 mL would over-anticoagulate the smaller plasma volume and falsely prolong clotting times.
A patient's prolonged aPTT shortens markedly when plasma is pre-incubated with the silica activator for 10 minutes instead of 3. Which deficiency is most likely?
In prekallikrein deficiency, factor XII slowly auto-activates with longer contact time, correcting the aPTT. Deficiencies of XI, IX or VIII do not correct this way.
A sample drawn from a central line shows a very prolonged thrombin time but a normal reptilase time. The most likely cause is:
Reptilase is not inhibited by heparin, so a normal reptilase with long TT indicates heparin. Low or abnormal fibrinogen prolongs both tests.
A patient with mild bleeding has mild thrombocytopenia, low VWF:Rco/VWF:Ag ratio and increased platelet aggregation with low-dose ristocetin. The most likely vWD type is:
Type 2B VWF binds platelet GPIb too strongly, giving enhanced low-dose RIPA and clearance of platelets. Type 2A shows reduced aggregation with ristocetin.
Before emergency surgery, a patient on dabigatran has a normal thrombin time. This most likely means:
The TT is very sensitive to direct thrombin inhibitors; a normal TT effectively excludes significant dabigatran. Even low levels markedly prolong it, so it cannot quantify therapeutic levels.
A healthy term newborn has platelets of 15 × 10^9/L and petechiae. The mother's platelet count is normal and she is HPA-1a negative. The most likely diagnosis is:
Maternal alloantibodies to fetal HPA-1a cross the placenta and destroy fetal platelets. In maternal ITP the mother herself is usually thrombocytopenic.