Acute Kidney Injury

Common in hospitalized patients, increasing in incidence,
and associated with adverse outcomes.
But, hard to identify.

Why AKI is Important


Acute kidney injury (AKI) is a rapid loss of kidney function which typically happens as a complication of another serious illness or intervention. Because pain and other symptoms don’t usually occur, AKI can be difficult to identify, but to preserve kidney function it is essential that AKI is detected early and treated promptly.

Identification and management of AKI is important as it is associated with negative outcomes, including:

Longer length of hospital stayi,iv

Increased use of renal replacement therapyi

Prolonged time on mechanical ventilationi

Higher risk of 28 day mortalityi,ii,iii

There is no specific treatment for AKI, making rapid identification of patients who are at risk critical.


Classification Systems for AKI

The definition of AKI, previously known as acute renal failure (ARF), has evolved for nearly two decades, as clinicians have struggled to classify the condition.v Since 2004, guidelines to standardize the definition, risk assessment, evaluation, prevention, and treatment of AKI have evolved:

  • Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease: RIFLE (2004)
  • Acute Kidney Injury Network: AKIN (2007)
  • Kidney Disease Improving Global Outcomes Criteria: KDIGO (2012)

The current KDIGO definition and staging of AKI is summarized in the table below.

KDIGO - Kidney Disease Improving Global Outcomes Criteria
Stage Serum CreatinineUrine Output Criteria
One1.5–1.9 times baseline,
or ≥0.3 mg/dL increase
<0.5 mL/kg/h for 6-12h
Two2–2.9 times baseline<0.5 mL/kg/h for ≥12h
Three3 times baseline, OR
Increase in serum creatinine to ≥4 mg/dL,
OR Initiation of renal replacement therapy
<0.3 mL/kg/h for ≥24h,
or anuria for ≥12h


i Kaddourah A, Basu RK, Bagshaw SM, Goldstein SL; AWARE Investigators. Epidemiology of Acute Kidney Injury in Critically Ill Children and Young Adults. N Engl J Med. 2017;376(1):11–20.

ii Susantitaphong P, Cruz DN, Cerda J, et al. World incidence of AKI: a meta-analysis Clin J Am Soc Nephrol. 2013;8(9):1482–1493.

iii Murugan R, Kellum JA. Acute kidney injury: what’s the prognosis?. Nat Rev Nephrol. 2011;7(4):209–217.

ivVarnell CD Jr, Goldstein SL, Devarajan P, Basu RK. Impact of Near Real-Time Urine Neutrophil Gelatinase-Associated Lipocalin Assessment on Clinical Practice. Kidney Int Rep. 2017;2(6):1243–1249.

v Kellum JA1, Levin N, Bouman C, Lameire N. Developing a consensus classification system for acute renal failure. Curr Opin Crit Care. 2002 Dec;8(6):509-14.

vi Ostermann M, Zarbock A, Goldstein S, et. al. Recommendations on Acute Kidney Injury Biomarkers From the Acute Disease Quality Initiative Consensus Conference: A Consensus Statement. JAMA Netw Open. 2020.