RIFLE vs KDIGO staging. Both systems stage by creatinine rise or urine output fall. KDIGO added the 0.3 mg/dL within-48h criterion (Stage 1) and dropped RIFLE's outcome stages (Loss, ESRD). In clinical practice and PG exams, knowing both is expected — particularly the Stage 3 / Failure thresholds and the RRT trigger.
FENa interpretation in AKI. The formula uses spot urine and plasma values for both sodium and creatinine. Key caveat: diuretics falsely raise FENa even in pre-renal states — use FE-Urea (<35% = pre-renal) instead in patients on diuretics.