Renal Medicine

Development and structure

• Ureteric bud forms ureter, pelvis, calyces and collecting ducts; metanephric mesenchyme forms nephron through distal tubule.
• Bilateral renal agenesis causes severe oligohydramnios and Potter sequence; horseshoe kidney is trapped during ascent.
• Filtration barrier: fenestrated endothelium, GBM and podocyte slit diaphragm.
• Juxtamedullary nephrons and vasa recta are essential for urine concentration.
• The JGA links tubular salt delivery and perfusion pressure to renin release.

Function and urine clues

• Creatinine clearance slightly overestimates GFR because of tubular secretion.
• Trimethoprim can raise creatinine without true GFR fall by inhibiting secretion.
• eGFR equations assume steady state and are unreliable in evolving AKI.
• Use A1, A2 and A3 albuminuria categories; avoid the old “microalbuminuria” wording.
• RBC casts suggest glomerular bleeding; muddy-brown casts suggest acute tubular injury; fatty casts suggest nephrotic lipiduria.
• Dipstick heme with few or no RBCs suggests myoglobin or haemoglobin.

Glomerular and vascular anchors

• Renal artery stenosis clues: resistant or abrupt hypertension, flash pulmonary oedema, asymmetric kidneys, abdominal bruit, or creatinine rise after ACEi/ARB.
• TMA is thrombocytopenia plus microangiopathic haemolysis with schistocytes, often with organ injury.
• MCD: near-normal LM, negative or minimal IF, diffuse foot-process effacement.
• FSGS is a pattern; classify primary, adaptive, genetic or secondary before immunosuppression.
• Membranous nephropathy: subepithelial deposits, granular capillary IF and PLA2R in many primary cases.
• IgA nephropathy is often synpharyngitic; PSGN follows a latent interval and often has low C3.
• Anti-GBM disease gives linear IgG and may cause pulmonary–renal emergency.

AKI, CKD and replacement

• AKI criteria: creatinine rise 0.3 mg/dL in 48 hours, 1.5 times baseline in 7 days, or urine output under 0.5 mL/kg/hour for 6 hours.
• Treat AKI emergencies first: hyperkalaemia, pulmonary oedema, severe acidosis, uraemic complications, obstruction and sepsis.
• CKD needs at least 3 months and is classified by cause, GFR category and albuminuria category.
• SGLT2 inhibitor therapy is kidney-protective in eligible CKD; hold during prolonged fasting, surgery or critical illness.
• ESA therapy should not maintain Hb at 11.5 g/dL or higher.
• Dialysis begins for complications, symptoms or trajectory, not an isolated creatinine, urea or eGFR number.
• Preferred routine tunneled dialysis catheter site is usually the right internal jugular vein; avoid subclavian when possible.
• PD peritonitis clue: cloudy effluent or abdominal pain; sample and treat promptly.