Year in review 2007: Critical Care – nephrology

Table 1 Classification/staging system for acute kidney injury

System	Class/stage	Serum creatinine criteria	Urine output criteria
RIFLE	Class R	Serum creatinine increase to 1.5-fold or GFR decrease >25% from baseline	<0.5 ml/kg/hour for 6 hours
	Class I	Serum creatinine increase to 2-fold or GFR decrease >50% from baseline	<0.5 ml/kg/hour for 12 hours
	Class F	Serum creatinine to 3-fold, GFR decrease >75% from baseline or serum creatinine ≥ 4 mg/dl (≥ 354 μmol/l) with an acute increase of at least 0.5 mg/dl (44 μmol/l)	Anuria for 12 hours
AKIN	Stage 1	Serum creatinine increase ≥ 0.3 mg/dl (≥ 26.4 μmol/l) or increase to 1.5-fold to 2-fold from baseline	<0.5 ml/kg per hour for 6 hours
	Stage 2	Serum creatinine increase >2-fold to 3-fold from baseline	<0.5 ml/kg per hour for 12 hours
	Stage 3	Serum creatinine increase >3-fold from baseline or serum creatinine ≥ 4.0 mg/dl (≥ 354 μmol/l) with an acute increase of at least 0.5 mg/dl (44 μmol/l)	<0.3 ml/kg per hour for 24 hours or anuria for 12 hours
		Need for RRT

Synopsis of RIFLE and AKIN criteria for AKI classification/staging. Small but significant changes can be identified between the two definitions. A time constraint of 48 hours for diagnosis (creatinine or urine output modifications) is required in AKIN criteria. GFR decreases for diagnosis are specified only by RIFLE. In both cases, only one criterion – creatinine or urine output – must be fulfilled to qualify for a class/stage. Classes L (loss of function) and E (end-stage kidney disease) of the RIFLE criteria are not reported. Given the wide variation in indications and timing of initiation of RRT, individuals who receive RRT are considered to have met the criteria for AKIN stage 3 irrespective of the stage they are in at the time of RRT. From Bellomo and coworkers [4] and Mehta and colleagues [5]. AKI, acute kidney injury; AKIN, Acute Kidney Injury Network; GFR, glomerular filtration rate; RIFLE, Risk, Injury, Failure, Loss and End-stage kidney disease; RRT, renal replacement therapy.

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