Every AKI must be classified: prerenal (60%), intrinsic (35%), or postrenal (5%). KDIGO 2012 · A

PRERENAL (most common — 60%):
• Volume depletion (hemorrhage, dehydration, GI losses)
• Low effective circulating volume (HF, cirrhosis, sepsis)
• FENa <1%, FEUrea <35%, BUN/Cr >20, urine Na <20
• Bland urine sediment. Responds to volume within 24-48h.

INTRINSIC (35%):
• ATN: most common. Muddy brown granular casts. FENa >2%. From ischemia or toxins.
• AIN: drug-induced (NSAIDs, PPIs, antibiotics). WBC casts, eosinophils. Steroids may help.
• GN: RBC casts (pathognomonic), proteinuria, hematuria. URGENT biopsy. Treat cause.
• Vascular: TMA, renal vein thrombosis, cholesterol emboli (livedo, eosinophilia, post-cath).

POSTRENAL (5%):
• Hydronephrosis on US = obstruction until proven otherwise
• BPH (most common in men), stones, tumor, blood clots
• Must be BILATERAL obstruction (or obstruction of solitary kidney) to cause AKI
• Bladder scan: post-void residual >200mL → Foley catheter → if UO improves → obstruction confirmed

🧫 Local Antibiogram