NAC OSCE Clinical Reasoning & Diagnosis — Questions and Answers
Question 1: A 25-year-old woman presents with acute onset pleuritic chest pain, dyspnoea, and a history of oral contraceptive use. Which investigation should be ordered FIRST according to Canadian guidelines?
- CT pulmonary angiography (CTPA) after pre-test probability assessment using the Wells PE score (Correct answer)
- Ventilation-perfusion (V/Q) scan as first line
- Echocardiogram to rule out pericarditis
- Arterial blood gas as the definitive test
Correct answer: CT pulmonary angiography (CTPA) after pre-test probability assessment using the Wells PE score
Canadian guidelines recommend calculating the Wells PE score first; if score is high or D-dimer is elevated in low/intermediate probability, CTPA is the first-line imaging choice.
Question 2: A 60-year-old male smoker has a 3-month history of haemoptysis, weight loss, and a right upper lobe opacity on CXR. What is the MOST appropriate next investigation?
- CT chest with IV contrast followed by bronchoscopy or CT-guided biopsy (Correct answer)
- Sputum cytology as the definitive test
- Repeat CXR in 6 weeks
- PET scan as first-line imaging
Correct answer: CT chest with IV contrast followed by bronchoscopy or CT-guided biopsy
A suspicious lung mass in a smoker requires tissue diagnosis; CT chest provides detailed characterisation and guides biopsy strategy, consistent with Canadian lung cancer screening and diagnosis guidelines.
Question 3: A 45-year-old woman presents with fatigue, weight gain, cold intolerance, and constipation. Which single test is MOST appropriate to confirm the suspected diagnosis?
- TSH (thyroid-stimulating hormone) (Correct answer)
- Free T4 alone
- Anti-TPO antibodies
- T3 level
Correct answer: TSH (thyroid-stimulating hormone)
TSH is the most sensitive first-line test for hypothyroidism, consistent with Canadian guidelines; a high TSH with low free T4 confirms primary hypothyroidism.
Question 4: In a diabetic patient presenting with fever, flank pain, and costovertebral angle tenderness, what complication must be urgently ruled out?
- Emphysematous pyelonephritis requiring urgent CT and possibly nephrectomy (Correct answer)
- Simple cystitis treated with oral antibiotics
- Renal calculus requiring urology referral only
- Diabetic nephropathy exacerbation
Correct answer: Emphysematous pyelonephritis requiring urgent CT and possibly nephrectomy
Emphysematous pyelonephritis is a life-threatening gas-forming infection of the renal parenchyma occurring predominantly in diabetics; CT abdomen is required urgently, and management may include percutaneous drainage or nephrectomy.
Question 5: A newborn has persistent cyanosis that does not improve with supplemental oxygen. Which congenital cardiac lesion should be MOST suspected?
- Transposition of the great arteries (TGA) (Correct answer)
- Tetralogy of Fallot
- Ventricular septal defect
- Patent ductus arteriosus
Correct answer: Transposition of the great arteries (TGA)
TGA causes parallel rather than series circulation, so supplemental oxygen does not improve saturations; this hyperoxia test (nitrogen washout test) distinguishes cardiac from pulmonary causes of cyanosis.
Question 6: A 30-year-old woman has episodic hypertension, headache, palpitations, and diaphoresis. Which investigation is MOST appropriate to screen for phaeochromocytoma according to Canadian Endocrine Society guidelines?
- 24-hour urinary metanephrines or plasma free metanephrines (Correct answer)
- 24-hour urinary catecholamines alone
- Clonidine suppression test as first line
- MRI adrenal glands without biochemical confirmation
Correct answer: 24-hour urinary metanephrines or plasma free metanephrines
Canadian Endocrine Society guidelines recommend plasma free metanephrines or 24-hour urinary fractionated metanephrines as first-line biochemical screening for phaeochromocytoma due to superior sensitivity.
NAC OSCE Clinical Reasoning & Diagnosis
A 25-year-old woman presents with acute onset pleuritic chest pain, dyspnoea, and a history of oral contraceptive use.
Which investigation should be ordered FIRST according to Canadian guidelines?