Master Internal Medicine
for USMLE Step 2 CK

What the USMLE Step 2 CK Tests in Internal Medicine

Internal Medicine on USMLE Step 2 CK tests your ability to manage common and critical adult medical conditions across cardiology, pulmonology, gastroenterology, nephrology, endocrinology, rheumatology, infectious disease, and hematology. You must recognise classic presentations (e.g., chest pain, dyspnoea, jaundice, polyuria), select appropriate initial investigations (e.g., ECG, troponin, D-dimer, HbA1c, LFTs), and apply evidence-based management including first-line drugs (e.g., ACE inhibitors for hypertension, metformin for type 2 diabetes, PPIs for GERD). Emphasis is on diagnostic reasoning: distinguishing urgent from non-urgent conditions, knowing when to admit versus manage outpatient, and applying guidelines (e.g., CURB-65 for pneumonia, CHA2DS2-VASc for atrial fibrillation, Wells criteria for PE). You must also interpret lab values (e.g., creatinine clearance, INR, anion gap) and recognise complications (e.g., diabetic ketoacidosis, acute kidney injury).

High-Yield Concepts

• Acute Coronary Syndrome (ACS) Management: For STEMI: door-to-balloon time <90 min; give aspirin 300 mg, clopidogrel 600 mg, heparin, and primary PCI. For NSTEMI: risk stratify with GRACE score; high-risk (troponin rise, dynamic ST changes) get early invasive strategy within 24 h. Beta-blocker (metoprolol) and statin (atorvastatin 80 mg) are first-line. Avoid NSAIDs.
• Community-Acquired Pneumonia (CAP) Severity and Treatment: Use CURB-65: 1 point each for confusion, urea >7 mmol/L, RR ≥30, BP <90/60, age ≥65. Score 0-1: treat outpatient with amoxicillin 500 mg TDS or doxycycline. Score 2: admit; give co-amoxiclav plus clarithromycin. Score ≥3: severe; IV co-amoxiclav plus clarithromycin, consider ICU.
• Diabetic Ketoacidosis (DKA) Management: Diagnosis: glucose >13.9 mmol/L, pH <7.3, bicarbonate <15, ketonaemia. Management: IV normal saline 1 L over 1 h, then 0.45% saline at 250-500 mL/h; insulin infusion 0.1 U/kg/h; when glucose <13.9 mmol/L, add 5% dextrose. Monitor potassium: replace if <5.5 mmol/L. Correct bicarbonate only if pH <6.9.
• Chronic Kidney Disease (CKD) Staging and Management: eGFR (mL/min/1.73m2): Stage 1 ≥90, Stage 2 60-89, Stage 3a 45-59, Stage 3b 30-44, Stage 4 15-29, Stage 5 <15. First-line BP target <130/80 mmHg; use ACE inhibitor (ramipril) or ARB (losartan). Monitor for hyperkalaemia, anaemia (treat with erythropoietin if Hb <100 g/L), and renal bone disease (check PTH, treat with vitamin D).
• Heart Failure with Reduced Ejection Fraction (HFrEF): EF <40%. First-line: ACE inhibitor (e.g., ramipril) or ARNI (sacubitril/valsartan), beta-blocker (bisoprolol), and mineralocorticoid receptor antagonist (spironolactone). Add SGLT2 inhibitor (dapagliflozin) if NYHA II-IV. Loop diuretic (furosemide) for fluid overload. Avoid NSAIDs, calcium channel blockers (verapamil, diltiazem).
• Pulmonary Embolism (PE) Diagnosis and Treatment: Use Wells criteria: clinical signs of DVT (3 pts), PE as likely as other diagnosis (3), HR >100 (1.5), immobilisation/surgery (1.5), previous DVT/PE (1.5), haemoptysis (1), cancer (1). Score >4: high probability; do CT pulmonary angiogram. Treatment: low molecular weight heparin (enoxaparin 1.5 mg/kg daily) or rivaroxaban. For massive PE with shock: thrombolysis (alteplase).
• Acute Pancreatitis: Diagnosis and Severity: Diagnosis: two of three—epigastric pain, amylase/lipase >3x upper limit, imaging findings. Ranson criteria at admission: age >55, WBC >16, glucose >11 mmol/L, LDH >350, AST >250. At 48 h: haematocrit drop >10%, BUN rise >1.8, calcium <2 mmol/L, PaO2 <60, base deficit >4, fluid sequestration >6 L. Score ≥3: severe; aggressive IV fluids (Ringer's lactate), monitor for necrosis.
• Thyroid Function Test Interpretation: Primary hyperthyroidism: low TSH, high free T4. Subclinical: low TSH, normal T4. Primary hypothyroidism: high TSH, low T4. Subclinical: high TSH, normal T4. Central hypothyroidism: low TSH, low T4. Sick euthyroid syndrome: low T3, normal TSH. Treatment: hyperthyroidism—carbimazole or propylthiouracil; hypothyroidism—levothyroxine 1.6 mcg/kg/day.

Common Traps in Internal Medicine Questions

• Confusing compensated with decompensated respiratory acidosis: check bicarbonate—if high, it's chronic compensation; if normal, acute.
• Giving insulin before fluid in DKA: leads to hypokalaemia and cardiac arrest; always rehydrate first.
• Using CT head to rule out subarachnoid haemorrhage: relies on timing—within 6 hours sensitivity is high; after 6 hours, do lumbar puncture for xanthochromia.
• Forgetting to stop metformin in acute kidney injury or before contrast: risk of lactic acidosis; hold if eGFR <30 or if contrast planned.
• Treating asymptomatic bacteriuria in elderly or catheterised patients: only treat in pregnancy, before urological procedures, or if symptomatic.
• Assuming all chest pain with ST elevation is STEMI: pericarditis shows diffuse ST elevation with PR depression; treat with NSAIDs, not thrombolysis.

How to Revise Internal Medicine for the USMLE Step 2 CK

Prioritise high-prevalence conditions: ACS, heart failure, pneumonia, COPD exacerbation, DKA, CKD, and PE. Questions often present a clinical vignette with labs and vitals; you must identify the most likely diagnosis, next best step in management (e.g., order a test, start a drug, admit), or complication to avoid. Practise interpreting ABGs, ECG patterns (e.g., atrial fibrillation, left ventricular hypertrophy, ST-elevation), and chest X-rays (e.g., lobar consolidation, pneumothorax). Focus on guideline-driven decision points: when to use thrombolysis, when to start insulin, when to refer for dialysis. Review the latest ACC/AHA and NICE guidelines for key cut-off values (e.g., BP targets, HbA1c goals). Use question banks that require you to choose between similar management options (e.g., IV fluids vs. diuretics in heart failure vs. renal failure).

Practise it: MedLumen has 50 Internal Medicine questions for the USMLE Step 2 CK, each with a full explanation and references.