STP Clinical Sciences 3 — Questions and Answers
Question 1: A patient with chronic kidney disease has a GFR of 18 mL/min/1.73m². Which CKD stage does this represent?
- Stage 3b
- Stage 4 (Correct answer)
- Stage 5
- Stage 3a
Correct answer: Stage 4
CKD Stage 4 is defined by a GFR of 15-29 mL/min/1.73m², indicating severely decreased kidney function and approaching the threshold for renal replacement therapy.
Question 2: Which immunoglobulin class is the predominant antibody in seronegative rheumatoid arthritis that targets citrullinated peptides?
- IgM
- IgA
- IgE
- IgG (Correct answer)
Correct answer: IgG
Anti-citrullinated protein antibodies (ACPAs), including anti-CCP antibodies, are predominantly of the IgG class and are highly specific for rheumatoid arthritis.
Question 3: A 30-year-old male has hemoglobin electrophoresis showing: HbS 80%, HbF 18%, HbA2 2%, HbA absent. Which condition does this indicate?
- Sickle cell trait
- Sickle cell disease (HbSS)
- HbSC disease
- Sickle-beta thalassemia (S/β0) (Correct answer)
Correct answer: Sickle-beta thalassemia (S/β0)
HbS 80% with absent HbA and elevated HbF, with normal HbA2 is characteristic of sickle-beta-zero thalassemia, where no HbA is produced due to the absent beta-globin chain.
Question 4: In the interpretation of a Western blot for HIV confirmation, which bands must be present for a result to be considered positive per CDC criteria?
- At least one band from gp120, gp41, or p24 (Correct answer)
- Two or more bands including p31
- Any two bands of viral origin
- Bands at p17 and p55 only
Correct answer: At least one band from gp120, gp41, or p24
CDC criteria require at least two of the following bands for a positive HIV Western blot: gp160/120, gp41, and p24, but any single band from these key antigens requires additional testing.
Question 5: A coagulation screen shows: PT normal, APTT prolonged, 1:1 mix corrects the APTT. Which factor deficiency is most likely?
- Factor VIII deficiency (Correct answer)
- Lupus anticoagulant
- Factor V deficiency
- Factor VII deficiency
Correct answer: Factor VIII deficiency
Isolated prolonged APTT that corrects on 1:1 mixing indicates a factor deficiency (not inhibitor) in the intrinsic pathway; Factor VIII deficiency (hemophilia A) is the most common cause.
Question 6: Which specimen container with additive is the correct choice for measuring plasma fibrinogen levels?
- EDTA (purple top)
- Lithium heparin (green top)
- Sodium fluoride/oxalate (grey top)
- Sodium citrate (blue top) (Correct answer)
Correct answer: Sodium citrate (blue top)
Coagulation tests including fibrinogen require sodium citrate (blue top) tubes, which chelate calcium to prevent clotting while preserving coagulation factor activity.
Question 7: Troponin T levels in a patient are 52 ng/L at 0 hours and 58 ng/L at 3 hours. Using the ESC 0/3-hour rule-out algorithm, what is the interpretation?
- Rule-out NSTEMI — low risk discharge
- Observe — inconclusive result (Correct answer)
- Rule-in NSTEMI — urgent cardiology review
- Repeat at 6 hours required
Correct answer: Observe — inconclusive result
For rule-out, the initial hsTnT must be <5 ng/L, or <12 ng/L with delta <3 ng/L; this result does not meet rule-out or rule-in criteria so the patient falls in the observe zone.
STP Clinical Sciences 3
A patient with chronic kidney disease has a GFR of 18 mL/min/1.73m².
Which CKD stage does this represent?