Acute kidney injury staging
Formal Definition
A classification system (KDIGO) for acute kidney injury based on creatinine criteria and urine output; Stage 1: increase in creatinine 1.5-1.9x baseline or >=0.3 mg/dL increase within 48h; Stage 2: 2-2.9x baseline; Stage 3: 3x baseline or increase in creatinine >=4 mg/dL or initiation of renal replacement therapy.
How It's Used on the Ward
AKI stage or KDIGO stage — how bad the kidney injury is; determines urgency of workup and whether you need to involve nephrology.
Example
"Baseline creatinine 1.1, now 3.2 after 5 days of vancomycin. KDIGO Stage 3 AKI. Nephrology consulted. Holding vancomycin, pending drug levels. Ultrasound ordered to rule out post-renal obstruction. Calculating FeNa, Urine Osm, fractional excretion of sodium to determine etiology."
Clinical Context
KDIGO stages 1-3: based on creatinine rise OR urine output. Urine output: <0.5 mL/kg/h for 6-12h (stage 1), 12-24h (stage 2), >=24h (stage 3). Etiology workup: prerenal (BUN:Cr >20:1, FeNa <1%, low urine sodium), intrinsic (FeNa >2%, active sediment), post-renal (obstruction → imaging). Common causes: ATN from ischemia/nephrotoxins, AIN (drug-induced: PPIs, NSAIDs, fluoroquinolones, beta-lactam), glomerular (RPGN). Nephrology consult: stage 3, refractory hyperkalemia, volume overload, metabolic acidosis, suspected obstruction.