Master Renal Medicine
for MRCP Part 1

Core Concepts

Renal medicine focuses on kidney function, disorders, and their management. Key concepts include:

• Glomerular Filtration Rate (GFR): Best measure of kidney function. Estimated by eGFR (MDRD, CKD-EPI equations), based on serum creatinine, age, sex, race. Normal >90 mL/min/1.73m².
• Acute Kidney Injury (AKI): Abrupt decline in kidney function over hours to days, characterized by increase in serum creatinine and/or reduction in urine output. Classified by KDIGO criteria (Stage 1, 2, 3).
• Chronic Kidney Disease (CKD): Kidney damage or decreased GFR (<60 mL/min/1.73m²) for >3 months. Staged by GFR (G1-G5) and albuminuria (A1-A3).
• Nephrotic Syndrome: Characterized by massive proteinuria (>3.5g/day), hypoalbuminemia, generalized edema, and hyperlipidemia. Minimal change disease is commonest cause in children; FSGS, membranous nephropathy in adults.
• Nephritic Syndrome: Characterized by hematuria (often microscopic, with red cell casts), proteinuria (sub-nephrotic), hypertension, and acute kidney injury. Post-streptococcal GN is a classic example.
• Electrolyte and Acid-Base Balance: Kidneys play crucial roles in regulating sodium, potassium, calcium, phosphate, and acid-base status. Imbalances are common in renal disease.
• Renal Tubular Acidosis (RTA): Disorders affecting tubular reabsorption/secretion of acid or bicarbonate. Type 1 (distal), Type 2 (proximal), Type 4 (hypoaldosteronism).

Clinical Presentation

• AKI: Oliguria/anuria, peripheral/pulmonary edema, nausea, fatigue, confusion (uremic symptoms), electrolyte disturbances (hyperkalemia).
• CKD: Often asymptomatic until advanced stages. Symptoms include fatigue, pruritus, anorexia, nausea, bone pain, muscle cramps, peripheral neuropathy, dyspnea (anemia, fluid overload), hypertension.
• Glomerulonephritis: Hematuria (cola-colored urine), edema, hypertension, frothy urine (proteinuria). Rapidly progressive GN (RPGN) presents with swift decline in GFR.
• Pyelonephritis: Fever, chills, flank pain, dysuria, frequency, urgency, nausea/vomiting.
• Nephrolithiasis (Kidney Stones): Acute severe flank pain radiating to groin, hematuria, nausea, vomiting.
• Polycystic Kidney Disease (ADPKD): Flank pain, hematuria, recurrent UTIs, hypertension. Extra-renal manifestations include liver cysts, berry aneurysms.
• Renal Artery Stenosis: Resistant hypertension, flash pulmonary edema, AKI upon ACEi/ARB initiation.
• Vasculitis: Systemic features (fever, rash, arthralgia) with rapidly deteriorating renal function (glomerulonephritis).

Diagnosis (Gold Standard)

• AKI: Trend of serum creatinine and urine output. Underlying cause often requires further investigation, e.g., renal ultrasound (for obstruction), urinalysis (casts, proteinuria), sometimes renal biopsy.
• CKD: eGFR calculation (MDRD/CKD-EPI) and albuminuria (urine ACR) over 3+ months. Renal ultrasound to assess kidney size/scarring.
• Glomerulonephritis: Renal biopsy (light microscopy, immunofluorescence, electron microscopy) is the gold standard for specific diagnosis. Urinalysis, ANCA, anti-GBM, ANA, complement levels aid initial workup.
• RTA: Blood gas, serum electrolytes, urine pH, urine anion gap, urine osmolality, ammonium excretion.
• Renal Artery Stenosis: CT Angiography or MR Angiography (definitive). Renal Doppler ultrasound is a good screening tool.
• ADPKD: Renal ultrasound or CT scan (shows multiple renal and often hepatic cysts).
• Urinary Tract Obstruction: Renal ultrasound is the initial investigation of choice.
• Multiple Myeloma Kidney: Serum/urine electrophoresis, free light chain assay. Renal biopsy may show cast nephropathy.

Management (First Line)

• AKI: Treat underlying cause (e.g., fluid resuscitation for pre-renal, relieve obstruction for post-renal). Withdraw nephrotoxic drugs. Strict fluid balance. Correct electrolyte imbalances (e.g., hyperkalemia). Renal replacement therapy (RRT) if indicated (AEIOU: Acidosis, Electrolytes, Intoxication, Overload, Uremia).
• CKD:
  • Blood Pressure Control: Target <130/80 mmHg (especially with albuminuria). ACE inhibitors or ARBs are first-line, particularly with proteinuria, but monitor K+ and Cr.
  • Glycemic Control: Strict control for diabetics.
  • Anemia: Iron supplementation, Erythropoiesis-stimulating agents (ESAs) if Hb <10 g/dL.
  • CKD-Mineral and Bone Disorder (CKD-MBD): Phosphate binders, active Vitamin D analogs.
  • Dietary modifications (low salt, low phosphate, low potassium).
  • Vaccinations (influenza, pneumococcal).
  • Referral for RRT planning (dialysis, transplantation) when eGFR <20-25 mL/min.
• Glomerulonephritis: Immunosuppression (e.g., corticosteroids, cyclophosphamide, rituximab) depending on specific diagnosis and severity. Plasma exchange for severe anti-GBM disease or some vasculitides.
• Hyperkalemia: Acute treatment: IV Calcium Gluconate (cardiac stabilization), IV Insulin/Glucose, Salbutamol nebuliser, loop diuretics. Chronic: Potassium binders (e.g., patiromer, sodium zirconium cyclosilicate).
• Nephrolithiasis: Hydration, analgesia. Alpha-blockers (e.g., tamsulosin) for distal ureteric stones. Extracorporeal shockwave lithotripsy (ESWL), ureteroscopy, or percutaneous nephrolithotomy (PCNL) for larger/obstructive stones.
• Hyponatremia: Fluid restriction if hyper/euvolemic. Hypertonic saline for severe symptomatic hyponatremia.