STP Clinical Sciences 4 — Questions and Answers
Question 1: A 25-year-old woman has a positive lupus anticoagulant, elevated anti-cardiolipin IgG, and a history of recurrent miscarriages. Her APTT does not correct on 1:1 mixing. Which diagnosis is most consistent?
- Inherited thrombophilia
- Antiphospholipid syndrome (Correct answer)
- von Willebrand disease type 1
- Hemophilia A carrier
Correct answer: Antiphospholipid syndrome
Antiphospholipid syndrome is characterized by antiphospholipid antibodies (lupus anticoagulant, anti-cardiolipin) causing thrombosis and pregnancy morbidity, with non-correcting APTT confirming an inhibitor.
Question 2: In the context of clinical pharmacology, which pharmacokinetic parameter describes the volume of fluid required to contain all of the drug in the body at the observed plasma concentration?
- Clearance
- Volume of distribution (Correct answer)
- Bioavailability
- Half-life
Correct answer: Volume of distribution
Volume of distribution (Vd) is a theoretical volume that relates total drug in the body to plasma concentration; a high Vd indicates extensive tissue distribution.
Question 3: A patient has sodium 128 mmol/L, urine osmolality 520 mOsm/kg, urine sodium 55 mmol/L, and normal thyroid/adrenal function. Which condition best explains these findings?
- Psychogenic polydipsia
- SIADH (Correct answer)
- Cerebral salt wasting
- Addison's disease
Correct answer: SIADH
SIADH presents with euvolemic hyponatremia, inappropriately elevated urine osmolality (>100 mOsm/kg), and elevated urine sodium (>20 mmol/L) with normal thyroid and adrenal function.
Question 4: Which PCR technique allows simultaneous quantification of multiple target sequences in a single reaction by using different fluorescent probes?
- Digital PCR
- Nested PCR
- Multiplex real-time PCR (Correct answer)
- Reverse transcription PCR
Correct answer: Multiplex real-time PCR
Multiplex real-time PCR uses multiple primer pairs and fluorescent probes with distinct emission wavelengths to simultaneously detect and quantify several targets in one reaction.
Question 5: In immunohistochemistry, heat-induced epitope retrieval (HIER) is used primarily to overcome which problem?
- Endogenous peroxidase activity
- Non-specific antibody binding
- Antigen masking by formalin cross-links (Correct answer)
- Tissue autofluorescence
Correct answer: Antigen masking by formalin cross-links
Formalin fixation creates protein cross-links that mask antigenic epitopes; HIER uses heat and buffer to break these cross-links and restore antigen-antibody binding capacity.
Question 6: A newborn screening program detects elevated phenylalanine on a dried blood spot at day 5. Which metabolic disorder must be excluded first?
- Maple syrup urine disease
- Homocystinuria
- Phenylketonuria (PKU) (Correct answer)
- Tyrosinemia type I
Correct answer: Phenylketonuria (PKU)
Elevated phenylalanine on newborn dried blood spot screening is the primary marker for PKU, caused by phenylalanine hydroxylase deficiency, requiring prompt dietary intervention to prevent intellectual disability.
Question 7: Which haematological finding on peripheral blood film is characteristic of hyposplenism?
- Schistocytes and helmet cells
- Howell-Jolly bodies and target cells (Correct answer)
- Hypersegmented neutrophils and macro-ovalocytes
- Tear drop cells and nucleated red cells
Correct answer: Howell-Jolly bodies and target cells
Howell-Jolly bodies (nuclear remnants) and target cells are characteristic of hyposplenism, as the spleen normally removes these erythrocyte inclusions; their persistence indicates splenic dysfunction.
STP Clinical Sciences 4
A 25-year-old woman has a positive lupus anticoagulant, elevated anti-cardiolipin IgG, and a history of recurrent miscarriages.
Her APTT does not correct on 1:1 mixing.
Which diagnosis is most consistent?