Pathophysiology
Clinical meaning
AKI KDIGO staging: Stage 1 (Cr 1.5-1.9x baseline or >=0.3 increase in 48h), Stage 2 (2-2.9x), Stage 3 (>=3x or Cr >4.0 or dialysis initiation). Prerenal (60-70%): decreased perfusion (FENa <1%, BUN:Cr >20:1). Intrinsic (25-30%): ATN (muddy brown casts, FENa >2%), GN (RBC casts), AIN (eosinophils, WBC casts). Postrenal (5-10%): obstruction (hydronephrosis on ultrasound).