Master Renal Medicine
for MRCP Part 1

What the MRCP Part 1 Tests in Renal Medicine

MRCP Part 1 Renal Medicine tests the ability to diagnose and manage acute kidney injury (AKI), chronic kidney disease (CKD), glomerulonephritis, tubular disorders, and electrolyte/acid-base disturbances. Candidates must apply KDIGO AKI criteria (creatinine rise ≥26.5 µmol/L in 48h or ≥1.5× baseline within 7 days), differentiate prerenal from intrinsic AKI using urine sodium (<20 mmol/L prerenal, >40 mmol/L intrinsic) and fractional excretion of sodium (FENa <1% prerenal, >2% intrinsic). They must know CKD staging by eGFR (G1 ≥90, G2 60-89, G3a 45-59, G3b 30-44, G4 15-29, G5 <15 mL/min/1.73m²) and albuminuria categories (A1 <3, A2 3-30, A3 >30 mg/mmol). Questions often present with urinalysis, renal biopsy results, or acid-base nomograms. Emphasis is on first-line treatments: ACEi/ARB for proteinuric CKD, steroids for minimal change disease, rituximab for ANCA vasculitis, and managing complications like hyperkalaemia (calcium gluconate, insulin/dextrose, salbutamol, then calcium resonium or patiromer).

High-Yield Concepts

• AKI Classification and Causes: KDIGO criteria: Stage 1: creatinine rise ≥26.5 µmol/L in 48h or 1.5-1.9× baseline; Stage 2: 2.0-2.9×; Stage 3: ≥3× or ≥353.6 µmol/L or initiation of RRT. Common prerenal causes: hypovolaemia, NSAIDs, ACEi. Intrinsic: acute tubular necrosis (ATN) from ischaemia or nephrotoxins (aminoglycosides, contrast), acute interstitial nephritis (AIN) from drugs (penicillins, PPIs, NSAIDs), glomerulonephritis. Postrenal: obstruction (BPH, stones, tumour).
• Nephrotic Syndrome Management: Defined by proteinuria >3.5 g/24h, hypoalbuminaemia <30 g/L, oedema, hyperlipidaemia. First-line for minimal change disease: prednisolone 1 mg/kg/day (max 80 mg) for 4-16 weeks. For membranous nephropathy: conservative (ACEi, statins) plus rituximab 1 g IV on days 1 and 15 if PLA2R antibody-positive. Focal segmental glomerulosclerosis (FSGS): steroids for primary, but often resistant; consider calcineurin inhibitors. Anticoagulate if albumin <20 g/L due to thromboembolism risk.
• ANCA-Associated Vasculitis and RPGN: Rapidly progressive glomerulonephritis (RPGN) presents with haematuria, red cell casts, crescents on biopsy. Anti-GBM disease: plasma exchange, cyclophosphamide, steroids. ANCA vasculitis (granulomatosis with polyangiitis, microscopic polyangiitis): induction with cyclophosphamide or rituximab plus high-dose steroids; maintenance with azathioprine or rituximab. Check ANCA (c-ANCA/PR3 in GPA, p-ANCA/MPO in MPA).
• Electrolyte Emergencies: Hyperkalaemia: Life-threatening if K+ >6.5 mmol/L or ECG changes (peaked T waves, loss of P wave, widened QRS). Immediate: 10 mL 10% calcium gluconate IV over 2-3 min (cardioprotection). Then shift K+ intracellularly: 10 units Actrapid insulin + 50 mL 50% dextrose IV over 15 min; salbutamol 5 mg nebulised. Remove K+: calcium resonium 15 g oral/PR, or patiromer, or haemodialysis if severe/refractory.
• Metabolic Acidosis: AG and Non-AG: Calculate anion gap (AG = Na - [Cl + HCO3]; normal 8-12). High AG acidosis: MUDPILES (methanol, uraemia, DKA, propylene glycol, isoniazid, lactate, ethylene glycol, salicylates). Non-AG (hyperchloraemic) acidosis: renal tubular acidosis (RTA), diarrhoea, acetazolamide. RTA type 1 (distal): hypokalaemia, nephrocalcinosis, urine pH >5.5. RTA type 2 (proximal): hypokalaemia, Fanconi syndrome (glycosuria, phosphaturia, aminoaciduria). RTA type 4: hyperkalaemia, hypoaldosteronism (e.g., DM, ACEi).
• CKD-MBD and Anaemia Management: CKD-mineral bone disorder: monitor Ca, PO4, PTH, vitamin D. Treat hyperphosphataemia with dietary restriction and phosphate binders (calcium acetate, sevelamer, lanthanum). For secondary hyperparathyroidism, use active vitamin D (calcitriol) or cinacalcet. Renal anaemia: target Hb 100-120 g/L; give IV iron if ferritin <100 µg/L or TSAT <20%; start ESA (epoetin alfa or darbepoetin) if Hb <100 g/L after iron repletion.
• Renal Replacement Therapy Indications: AEIOU: Acidosis (pH <7.15), Electrolytes (K+ >6.5 refractory), Intoxications (lithium, methanol, ethylene glycol, salicylates), Overload (pulmonary oedema unresponsive to diuretics), Uraemia (pericarditis, encephalopathy, bleeding). Also consider when creatinine >800 µmol/L or eGFR <10 mL/min/1.73m² in CKD. Modalities: haemodialysis, peritoneal dialysis, or haemofiltration in ICU.
• Hereditary Renal Diseases: Autosomal dominant polycystic kidney disease (ADPKD): PKD1 or PKD2 mutation; presents with hypertension, haematuria, flank pain, recurrent UTIs; screen for berry aneurysms. Alport syndrome: X-linked COL4A5 mutation; sensorineural deafness, lenticonus, progressive CKD; no specific treatment, ACEi slows progression. Fabry disease: X-linked α-galactosidase A deficiency; acroparesthesias, angiokeratomas, corneal opacities, CKD; treat with agalsidase alfa/beta enzyme replacement.

Common Traps in Renal Medicine Questions

• Confusing prerenal AKI with ATN: prerenal has low urine Na (<20) and FENa <1%, while ATN has high urine Na (>40) and FENa >2%.
• Assuming all hyperkalaemia with ECG changes can wait for lab confirmation: give calcium gluconate immediately if ECG abnormal or K+ >6.5 mmol/L.
• Mistaking nephritic syndrome (haematuria, hypertension, oliguria, red cell casts) for nephrotic syndrome (heavy proteinuria, oedema, hypoalbuminaemia) — they have different management.
• Forgetting that ACEi/ARB can cause acute rise in creatinine (up to 30%) which is acceptable and not a reason to stop unless rise >50% or hyperkalaemia develops.
• Thinking that renal biopsy is contraindicated if single kidney or eGFR <30 — it is possible with careful planning (e.g., transjugular approach) but higher risk.
• Overlooking that in type 4 RTA (hyperkalaemic metabolic acidosis), the primary defect is hypoaldosteronism; treat with fludrocortisone if not volume-overloaded.

How to Revise Renal Medicine for the MRCP Part 1

Focus on acute scenarios: AKI with drug history (NSAIDs, ACEi, aminoglycosides), glomerulonephritis presenting with haematuria and proteinuria, and electrolyte crises. Practice interpreting ABG and renal function trends quickly. Questions often give a vignette with urine dipstick, serum creatinine, and potassium; you must decide next step (e.g., fluid challenge vs. stop nephrotoxin vs. biopsy vs. dialysis). Memorise key cut-offs: K+ >6.5 for emergency, creatinine rise criteria for AKI staging, eGFR thresholds for drug dosing (e.g., metformin stop at eGFR <30, DOACs adjust at <15-30). Revise drug nephrotoxicity: lithium (nephrogenic DI), tenofovir (Fanconi), cisplatin (ATN), calcineurin inhibitors (hypertension, hyperkalaemia). Use question banks with clinical reasoning; expect 2-3 questions on acid-base and 2-3 on glomerular disease per paper. Prioritise understanding pathophysiology over rare syndromes.

Practise it: MedLumen has 50 Renal Medicine questions for the MRCP Part 1, each with a full explanation and references.