Master Basic Medical Sciences
for SMLE

What the SMLE Tests in Basic Medical Sciences

The SMLE Basic Medical Sciences section tests applied physiology, pathology, pharmacology, and biochemistry in clinical contexts. Candidates must interpret presenting complaints (e.g., chest pain, jaundice, polyuria) and select appropriate diagnostics, first-line treatments, or identify underlying mechanisms. Emphasis is on linking molecular or cellular pathology to bedside decisions—for example, recognising that a patient with microcytic anaemia and normal ferritin may have anaemia of chronic disease (hepcidin-driven) rather than iron deficiency. You must know WHO diagnostic criteria for diabetes (fasting glucose ≥7.0 mmol/L, HbA1c ≥48 mmol/mol), GOLD stages for COPD (FEV1/FVC <0.70 post-bronchodilator), and NICE guidelines for hypertension (target <140/90 mmHg). Questions often present a scenario with lab values or imaging findings and ask for the most likely diagnosis, the mechanism of drug action, or the next best step in management. Drug interactions (e.g., warfarin and amiodarone) and side-effect profiles (e.g., ACE inhibitors causing cough) are frequently tested.

High-Yield Concepts

• Anaemia Classification: Microcytic anaemia (MCV <80 fL): iron deficiency (low ferritin, low transferrin saturation), thalassaemia trait (raised HbA2, normal ferritin), anaemia of chronic disease (normal/high ferritin). Macrocytic anaemia (MCV >100 fL): B12 deficiency (low B12, raised methylmalonic acid) or folate deficiency (low folate, normal methylmalonic acid). Always check reticulocyte count to distinguish hypoproliferative from haemolytic anaemia.
• Acid-Base Disorders: Use Winter's formula (expected PaCO2 = 1.5 × HCO3 + 8 ± 2) for metabolic acidosis. Anion gap = Na – (Cl + HCO3); normal 8–12 mmol/L. High anion gap metabolic acidosis (MUDPILES: methanol, uraemia, DKA, propylene glycol, isoniazid, lactic acidosis, ethanol, salicylates). Non-anion gap: diarrhoea, renal tubular acidosis. pH <7.35 = acidaemia; pH >7.45 = alkalaemia.
• Myocardial Infarction Diagnosis: Fourth Universal Definition: rise/fall of cardiac troponin with at least one of: symptoms of ischaemia, new ST-T changes or LBBB, pathological Q waves, imaging evidence of new loss of viable myocardium, or intracoronary thrombus. High-sensitivity troponin: 99th percentile upper reference limit (e.g., >34 ng/L for hs-cTnI). ECG: STEMI = ST elevation ≥1 mm in limb leads or ≥2 mm in precordial leads in two contiguous leads.
• Diabetes Mellitus Diagnostic Criteria: WHO 2019: fasting plasma glucose ≥7.0 mmol/L, or 2-hour glucose ≥11.1 mmol/L during 75 g OGTT, or HbA1c ≥48 mmol/mol (6.5%). For gestational diabetes: 75 g OGTT at 24–28 weeks, fasting ≥5.1, 1-hour ≥10.0, 2-hour ≥8.5 mmol/L. First-line metformin in type 2 unless eGFR <30 mL/min/1.73m².
• Chronic Kidney Disease Staging: Based on eGFR (CKD-EPI formula) and ACR (albumin:creatinine ratio). Stage 1: eGFR ≥90 + ACR ≥3 mg/mmol; Stage 2: 60–89 + ACR ≥3; Stage 3a: 45–59; Stage 3b: 30–44; Stage 4: 15–29; Stage 5: <15. Target BP <130/80 mmHg; first-line ACEi or ARB if ACR >3 mg/mmol.
• Antibiotic Mechanisms and Resistance: Beta-lactams (penicillins, cephalosporins) inhibit transpeptidase (penicillin-binding proteins); resistance via beta-lactamase (e.g., ESBL) or altered PBPs (MRSA). Macrolides (azithromycin) bind 50S ribosomal subunit. Fluoroquinolones (ciprofloxacin) inhibit DNA gyrase/topoisomerase IV. Vancomycin inhibits cell wall synthesis; resistance in enterococci (vanA/vanB). Always check local antibiogram.
• Liver Function Tests Interpretation: Hepatocellular pattern: raised ALT/AST (e.g., viral hepatitis, NAFLD). Cholestatic: raised ALP, GGT (e.g., gallstones, PBC). Mixed: both. Synthetic function: INR >1.5, albumin <35 g/L suggests cirrhosis. Child-Pugh score: bilirubin, albumin, INR, ascites, encephalopathy; Class A (5–6), B (7–9), C (10–15). MELD-Na for transplant listing.
• Pulmonary Function Tests in COPD: Post-bronchodilator FEV1/FVC <0.70 confirms airflow limitation. GOLD 1: FEV1 ≥80% predicted; GOLD 2: 50–79%; GOLD 3: 30–49%; GOLD 4: <30%. mMRC dyspnoea scale ≥2 or CAT score ≥10 indicates high symptom burden. First-line: LAMA/LABA combination; triple therapy (ICS/LAMA/LABA) if exacerbations ≥2/year or eosinophils ≥300 cells/µL.

Common Traps in Basic Medical Sciences Questions

• Assuming a low MCV always means iron deficiency without checking ferritin and transferrin saturation.
• Using the anion gap formula without correcting for albumin (corrected AG = AG + 0.25 × (40 – albumin)).
• Diagnosing STEMI based solely on troponin elevation without ECG criteria for ST elevation.
• Interpreting HbA1c in patients with haemoglobinopathies (e.g., sickle cell trait) or renal failure without using alternative markers (fructosamine).
• Forgetting that eGFR equations (CKD-EPI) are unreliable in acute kidney injury or extremes of muscle mass.
• Treating COPD exacerbations with high-dose steroids without checking for eosinopenia or fungal infection risk.

How to Revise Basic Medical Sciences for the SMLE

Prioritise high-yield clinical presentations that integrate pathophysiological reasoning: e.g., a patient with jaundice, dark urine, and pale stools (obstructive jaundice vs. hepatitis) with LFT pattern recognition. Practice interpreting lab panels (ABG, LFT, renal, coagulation) in a single scenario. Focus on NICE/WHO diagnostic cut-offs and first-line drug choices (e.g., ACEi for CKD with proteinuria, metformin for type 2 diabetes). Questions are often vignette-based with one key lab value or imaging finding; learn to spot the 'distractor' result. Use spaced repetition for drug mechanisms and side effects (e.g., statins and myopathy, metformin and lactic acidosis). Practise 20–30 timed multiple-choice questions daily, reviewing why each wrong answer is wrong.

Practise it: MedLumen has 50 Basic Medical Sciences questions for the SMLE, each with a full explanation and references.