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).
Diagnosis & workup
Diagnostics & workup: - Comprehensive metabolic panel (electrolytes, calcium, phosphorus, bicarbonate) - BUN/Creatinine ratio (>20:1 suggests prerenal etiology) - CBC for anemia of CKD evaluation - Serum creatinine with eGFR calculation (CKD-EPI equation) - Urinalysis with microscopy (casts, crystals, cells) - ANCA, anti-GBM, anti-dsDNA for autoimmune renal disease - Renal biopsy for unexplained proteinuria, hematuria, or AKI
Risk factors: - IV contrast administration (contrast-induced nephropathy) - Hypertension (second leading cause of CKD) - Nephrotoxic medications (aminoglycosides, vancomycin, amphotericin B) - Diabetes mellitus (leading cause of CKD, 44% of new ESRD) - Age >60 with age-related GFR decline - Volume depletion from any cause - Rhabdomyolysis from trauma, statins, or extreme exertion