Table 1.

AKIN staging system for AKI^*

Stage	Serum creatinine criteria	Urine output criteria
1	Increase in serum creatinine level of ≥25 μmol/l or ≥150–200% (1.5–2-fold) from baseline	Change in urine output <0.5 (ml/kg)/h for >6 h
2	Increase in serum creatinine level to >200–300% (>2–3-fold) from baseline	Change in urine output <0.5 (ml/kg)/h for >12 h
3	Increase in serum creatinine level to >300% (>threefold) from baseline (or serum; creatinine level of ≥354 μmol/l with an acute increase of at least 44 μmol/l	Change in urine output <0.3 (ml/kg)/h for 24 h or anuria for 12 h

^*The AKIN modification of RIFLE criteria¹⁹ is a highly sensitive staging system based on data indicating that a small change in serum creatinine influences outcome.²⁰ Only one criterion (serum creatinine level or urine output) has to be fulfilled to qualify for a stage. Given wide variation in indications and timing of initiation of renal replacement therapy, individuals who receive renal replacement therapy are considered to have met the criteria for stage 3 irrespective of the stage they are in at the time of initiation of renal replacement therapy. Abbreviations: AKI, acute kidney injury; AKIN, acute kidney injury network; RIFLE, Risk, Injury, Failure, Loss, and End-stage renal disease. Permission obtained from BioMed Central © Mehta, R.L. et al. Crit. Care 11, R31 (2007).