Table 4.

Acute kidney injury classification systems

System	Injury stage	Criteria (serum creatinine)	Criteria (urine output)
RIFLE	R (risk)	≥1.5-fold Cr increase or GFR decrease ≥ 25 %	<0.5 ml/kg/h for 6 h
	I (injury)	≥2-fold Cr increase or GFR decrease ≥ 50 %	<0.5 ml/kg/h for 12 h
	F (failure)	≥3-fold Cr increase or Cr >4.0 mg/dl	<0.3 ml/kg/h or anuria for 12 h
	L (loss)	Persistent failure >4 wk
	E (end stage)	Persistent failure >3 mo
pRIFLE	R (risk)	GFR decrease ≥ 25 %	<0.5 ml/kg/h for 6 h
	I (injury)	GFR decrease ≥ 50 %	<0.5 ml/kg/h for 12 h
	F (failure)	GFR decrease ≥ 75 % or eGFR < 35 ml/min/1.73 m2	<0.3 ml/kg/h or anuria for 12 h
	L (loss)	Persistent failure >4 wk
	E (end stage)	Persistent failure >3 mo
AKIN	Stage 1	≥ 0.3 mg/dl Cr increase or 150–200 % increase above baseline	<0.5 ml/kg/h for 6 h
	Stage 2	Cr increase of 200–300 % of baseline	<0.5 ml/kg/h for 12 h
	Stage 3	Cr increase ≥ 300 % of baseline or ≥4.0 mg/dl with an acute increase of 0.5 mg/dl	<0.3 ml/kg/h or anuria for 12 h
KDIGO	Stage 1	≥ 0.3 mg/dl Cr increase or 1.5–1.9 times baseline	<0.5 ml/kg/h for 6–12 h
	Stage 2	Cr increase of 2.0–2.9 times baseline	<0.5 ml/kg/h for ≥12 h
	Stage 3	Cr increase of 3.0 times baseline or Cr ≥4.0 mg/dl or initiation of renal replacement therapy or eGFR <35 ml/min per 1.73 m2 in patients <18 years	<0.3 ml/kg/h for ≥24 h or anuria for ≥12 h

AKIN, Acute Kidney Injury Network; KDIGO, Kidney Disease Improving Global Outcome; eGFR, estimated glomerular filtration rate