STP Clinical Sciences 5 — Questions and Answers
Question 1: A 60-year-old male has serum protein electrophoresis showing a monoclonal band in the gamma region. Serum free light chain ratio is 8.2 (normal 0.26-1.65). What additional investigation is most critical to differentiate MGUS from multiple myeloma?
- Bone marrow trephine biopsy (Correct answer)
- Serum beta-2 microglobulin
- 24-hour urine protein electrophoresis
- Full blood count
Correct answer: Bone marrow trephine biopsy
Bone marrow trephine biopsy is essential to quantify plasma cell percentage; multiple myeloma requires ≥10% clonal plasma cells plus myeloma-defining events, differentiating it from MGUS.
Question 2: In platelet function testing, a patient shows normal platelet aggregation with collagen but absent aggregation with ADP and absent second wave with epinephrine. Which disorder does this pattern suggest?
- Glanzmann thrombasthenia
- Bernard-Soulier syndrome
- ADP receptor (P2Y12) defect (Correct answer)
- Storage pool disease
Correct answer: ADP receptor (P2Y12) defect
Absent ADP-induced aggregation and absence of the epinephrine second wave (which requires ADP amplification) with normal collagen aggregation is the hallmark pattern of P2Y12 receptor deficiency.
Question 3: A reference interval study is performed on 200 healthy adults. Using a non-parametric method, what percentile range defines the standard reference interval?
- 5th to 95th percentile
- 2.5th to 97.5th percentile (Correct answer)
- 1st to 99th percentile
- 10th to 90th percentile
Correct answer: 2.5th to 97.5th percentile
The standard clinical reference interval encompasses the central 95% of the reference population, defined by the 2.5th to 97.5th percentiles using non-parametric or parametric methods per CLSI EP28-A3c.
Question 4: Which cytogenetic abnormality is the most common translocation found in acute promyelocytic leukemia (APL) and determines eligibility for ATRA therapy?
- t(9;22)(q34;q11)
- t(15;17)(q24;q21) (Correct answer)
- t(8;21)(q22;q22)
- inv(16)(p13q22)
Correct answer: t(15;17)(q24;q21)
The t(15;17) translocation creates the PML-RARA fusion gene in APL; this fusion protein drives the disease and is specifically targeted by all-trans retinoic acid (ATRA), which induces differentiation.
Question 5: A urine culture grows 10^5 CFU/mL of E. coli. The patient is asymptomatic. Which action is most appropriate according to UK clinical guidelines?
- Prescribe nitrofurantoin for 7 days
- Treat only if the patient is pregnant or pre-operative (Correct answer)
- Prescribe trimethoprim for 3 days
- Repeat culture and treat if confirmed
Correct answer: Treat only if the patient is pregnant or pre-operative
Asymptomatic bacteriuria should not be treated in most populations; UK guidelines recommend treatment only in pregnant women and patients undergoing urological procedures to prevent complications.
Question 6: In the liver function test panel, which enzyme elevation most specifically indicates cholestatic liver disease rather than hepatocellular damage?
- ALT (alanine aminotransferase)
- AST (aspartate aminotransferase)
- ALP (alkaline phosphatase) (Correct answer)
- LDH (lactate dehydrogenase)
Correct answer: ALP (alkaline phosphatase)
ALP (alkaline phosphatase) is localized to the bile canalicular membrane and is specifically elevated in cholestatic conditions; elevated ALP with raised GGT confirms biliary rather than bone origin.
Question 7: A researcher reports a new biomarker with an AUC (area under the ROC curve) of 0.95 for diagnosing sepsis. Which statement best describes this result?
- The biomarker correctly diagnoses sepsis in 95% of all patients tested
- The biomarker has 95% sensitivity and 95% specificity
- The biomarker has excellent discriminatory ability between sepsis and non-sepsis patients (Correct answer)
- The biomarker has a 95% positive predictive value
Correct answer: The biomarker has excellent discriminatory ability between sepsis and non-sepsis patients
An AUC of 0.95 indicates excellent overall discriminatory ability of the biomarker; AUC represents the probability that the biomarker ranks a random positive case higher than a random negative case.
STP Clinical Sciences 5
A 60-year-old male has serum protein electrophoresis showing a monoclonal band in the gamma region.
Serum free light chain ratio is 8.2 (normal 0.26-1.65).
What additional investigation is most critical to differentiate MGUS from multiple myeloma?