Medicine: Systematic Diagnosis and Safe Prescribing
Core content
Internal medicine questions reward a structured approach. You must recognise the classic presentations of cardiovascular, respiratory, endocrine, renal, gastrointestinal and haematological disease, and know first-line investigation and management. High-yield areas include ischaemic heart disease and heart failure, asthma and COPD, diabetes and thyroid disease, acute kidney injury, anaemia classification, and the recognition of life-threatening emergencies such as sepsis, diabetic ketoacidosis and pulmonary embolism.
Traps and discriminations
- Acute versus chronic. Many stems hinge on time course; a wheeze of two days differs from one of twenty years.
- Investigation hierarchy. The best initial test is often not the most definitive one. For suspected pulmonary embolism in a stable patient, follow the algorithm rather than jumping to the gold standard.
- Drug interactions and contraindications. Beta-blockers in asthma, NSAIDs in renal impairment, metformin and contrast, ACE inhibitors and hyperkalaemia are recurring themes.
- Anaemia morphology. Use mean corpuscular volume to narrow the differential before selecting a test; microcytic, normocytic and macrocytic lists are short and examinable.
- Look-alike presentations. Hyperthyroidism versus anxiety, heart failure versus COPD, and delirium versus dementia all appear as discriminators.
Worked example: the diagnostic sieve
A patient presents with confusion, polyuria and weight loss. Rule of thumb: check a capillary glucose immediately. If raised, measure ketones and a venous blood gas. A pH below 7.3 with ketonaemia confirms diabetic ketoacidosis, and management begins with fluids, insulin and potassium replacement, not bicarbonate. The trap is treating the glucose number alone and missing the potassium that will fall once insulin starts.
Prescribing safety
Know the common prescribing errors the exam tests: wrong dose in renal impairment, failure to review interacting medications, and omission of monitoring. Always ask what needs checking before and after a drug is started.