Internal Medicine
Core concepts
Internal medicine questions reward a disciplined approach: identify the syndrome, generate a short differential, and let the most specific finding discriminate. Master the classic patterns - heart failure (orthopnea, elevated JVP, S3, BNP), acute coronary syndrome (risk factors, ECG territory, troponin kinetics), COPD versus asthma (reversibility, smoking history, eosinophils), diabetes (diagnostic thresholds, complications), thyroid disease, and acid-base disorders. Also know the common electrolyte emergencies (hyperkalemia ECG changes, hyponatremia correction limits) and the criteria for community-acquired pneumonia severity.
Traps
Questions love the "most likely diagnosis" versus "next best step" distinction - one asks for reasoning, the other for management. Watch for anchoring on a single abnormal lab while ignoring the clinical picture. Acid-base items often require calculating the anion gap and the expected compensation; a normal pH does not exclude a mixed disorder. Another frequent trap is confusing nephrotic (proteinuria >3.5 g/day, edema, hypoalbuminemia) with nephritic (hematuria, RBC casts, hypertension) syndromes. Time-course stems matter: troponin rises over hours, so an early normal value does not exclude infarction.
Worked rule of thumb
For any acid-base stem, calculate in order: pH (acidemia vs alkalemia), then primary disorder from PaCO2 and HCO3, then anion gap (Na − [Cl + HCO3], normal ~8–12), then expected compensation. Example: pH 7.25, PaCO2 26, HCO3 11, Na 138, Cl 100. Acidemia with low HCO3 means metabolic acidosis; respiratory compensation is appropriate (expected PaCO2 ≈ 1.5×11+8 = 24.5, close to 26). Anion gap = 138 − 111 = 27, so a high-anion-gap acidosis (e.g., ketoacidosis, lactate, toxins, renal failure). That single sequence answers most stems.