Definition and staging criteria of acute kidney injury in adults up todate

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Definition and staging criteria of acute kidney injury in
adults
Author: Paul M Palevsky, MD
Section Editor: Gary C Curhan, MD, ScD
Deputy Editor: Shveta Motwani, MD, MMSc, FASN
All topics are updated as new evidence becomes available and our peer review process is complete.
Literature review current through: Apr 2021. | This topic last updated: Feb 09, 2021.
INTRODUCTION
Acute kidney injury (AKI) refers to an abrupt decrease in kidney function, resulting in the
retention of urea and other nitrogenous waste products and in the dysregulation of
extracellular volume and electrolytes. The term AKI has largely replaced acute renal failure
(ARF), reflecting the recognition that smaller decrements in kidney function that do not result in
overt organ failure are of substantial clinical relevance and are associated with increased
morbidity and mortality.
Several consensus definitions of AKI have been developed in order to provide a uniform
definition of AKI. These definitions are based exclusively upon the serum creatinine and urine
output and are used primarily to identify patients with AKI in epidemiologic and outcome
studies. The overall utility of these definitions and staging systems in the clinical assessment
and management of patients with AKI remains to be validated.
The potential etiologies, diagnosis, and management of AKI are discussed elsewhere:
®
(See "Etiology and diagnosis of prerenal disease and acute tubular necrosis in acute kidney
injury in adults".)
●
(See "Diagnostic approach to adult patients with subacute kidney injury in an outpatient
setting".)
●
(See "Overview of the management of acute kidney injury (AKI) in adults".)
●

DIAGNOSTIC CRITERIA
The definition for AKI used in clinical and epidemiologic studies is based on specific criteria that
have been sequentially developed. The Kidney Disease: Improving Global Outcomes (KDIGO)
definition and staging system is the most recent and preferred definition [1]. Other criteria
include the RIFLE criteria (Risk, Injury, Failure, Loss of kidney function, and End-stage kidney
disease) [2] and a subsequent modification proposed by the Acute Kidney Injury Network (AKIN)
and others [3-5]. These criteria are outlined in the table ( table 1).
The KDIGO guidelines define AKI as follows [1]:
The KDIGO criteria allow for correction of volume status and obstructive causes of AKI prior to
classification. Before diagnosing and classifying AKI, one should assess and optimize volume
status and exclude obstruction. This is based upon AKIN criteria, on which the KDIGO definition
is based. The AKIN state that these criteria should be used in the context of the clinical
presentation and following adequate fluid resuscitation, when applicable, and that use of the
urine output criteria alone requires exclusion of urinary tract obstruction or other easily
reversible causes of reduced urine output. (See "Evaluation of acute kidney injury among
hospitalized adult patients".)
The timeframe for an absolute increase in serum creatinine of ≥0.3 mg/dL is retained from the
AKIN definition (48 hours), while the timeframe for a ≥50 percent increase in serum creatinine
reverted to the seven days originally included in the Acute Dialysis Quality Initiative (ADQI) RIFLE
criteria.
The RIFLE and AKIN definitions are shown in the table ( table 1).
STAGING CRITERIA
Using the Kidney Disease: Improving Global Outcomes (KDIGO) criteria, AKI is staged as follows:
Increase in serum creatinine by ≥0.3 mg/dL (≥26.5 micromol/L) within 48 hours, or
●
Increase in serum creatinine to ≥1.5 times baseline, which is known or presumed to have
occurred within the prior seven days, or
●
Urine volume <0.5 mL/kg/hour for six hours
●
Stage 1 – Increase in serum creatinine to 1.5 to 1.9 times baseline, or increase in serum
creatinine by ≥0.3 mg/dL (≥26.5 micromol/L), or reduction in urine output to <0.5
●

The KDIGO criteria differ from the RIFLE classification in that the KDIGO criteria only utilize
changes in serum creatinine and urine output, not changes in GFR for staging, with the
exception of children under the age of 18 years, for whom an acute decrease in eGFR to <35
mL/min/1.73 m is included in the criteria for stage 3 AKI.
As with the RIFLE and Acute Kidney Injury Network (AKIN) staging systems, KDIGO suggested
that patients be classified according to criteria that result in the highest (ie, most severe) stage
of injury.
LIMITATIONS
There are a number of limitations to the Kidney Disease: Improving Global Outcomes (KDIGO)
criteria for AKI [6-9]. These limitations also apply to the older criteria (such as RIFLE and Acute
Kidney Injury Network [AKIN]) that also rely solely on changes in creatinine or urine output.
mL/kg/hour for 6 to 12 hours.
Stage 2 – Increase in serum creatinine to 2.0 to 2.9 times baseline, or reduction in urine
output to <0.5 mL/kg/hour for ≥12 hours.
●
Stage 3 – Increase in serum creatinine to 3.0 times baseline, or increase in serum creatinine
to ≥4.0 mg/dL (≥353.6 micromol/L), or reduction in urine output to <0.3 mL/kg/hour for ≥24
hours, or anuria for ≥12 hours, or the initiation of kidney replacement therapy, or, in
patients <18 years, decrease in estimated glomerular filtration rate (eGFR) to <35
mL/min/1.73 m .
●
2
2
Many etiologies cause AKI – A major flaw is that the criteria do not distinguish between
the multiple etiologies that cause AKI. It is incorrect to treat AKI as a single disease,
particularly grouping together hemodynamic causes (ie, "prerenal AKI") and acute tubular
necrosis. To address this, the KDIGO guidelines specified that patients with AKI be
evaluated promptly to determine cause [1]. Such evaluation is critical for patient care since
reversible causes of AKI (such as obstruction) require specific interventions.
●
In addition, different causes of AKI are associated with different long-term outcomes and
prognoses, which is not always addressed in studies that utilize AKI criteria.
Finally, from a research perspective, the development of therapeutic interventions requires
the addition of etiologic or anatomic diagnoses to the criteria [9].

Use of urine output to define AKI – Another important issue is the use of urine output as
a sole criterion for AKI. The KDIGO criteria define stages by change in either serum
creatinine or urine output. (See 'Diagnostic criteria' above.)
●
However, using urine output to define or stage AKI is not based on robust evidence. In one
assessment of the RIFLE classification, which compared the serum creatinine and urine
output criteria, the serum creatinine criteria were strong predictors of intensive care unit
(ICU) mortality, whereas the urine output criteria did not independently predict mortality
[10]. Brief durations of oliguria may just reflect insufficient volume resuscitation [7].
Other studies, however, have suggested that urine output is predictive of mortality [11,12],
and one study even suggested that urine output may be a more sensitive marker for AKI
than serum creatinine [13].
One study suggests that risks of death or kidney replacement therapy were highest when
both the serum creatinine and urine output criteria were met [14]. However, although the
criteria include both creatinine and urine output, in practice, the urine output is often
omitted from studies [6].
Until this issue is resolved, it is reasonable to use the criteria that result in the least
favorable strata assignment, as suggested in the Acute Dialysis Quality Initiative (ADQI)
group [2] and affirmed by KDIGO [1].
Determination of baseline creatinine – The determination of a baseline creatinine for
individual patients is a third limitation. It is impossible to calculate the change in serum
creatinine in patients who present with AKI but who do not have a baseline measurement
of serum creatinine.
●
The authors of the RIFLE criteria had initially suggested back-calculating an estimated
baseline serum creatinine concentration using the four-variable Modification of Diet in
Renal Disease (MDRD) equation, assuming a baseline glomerular filtration rate (GFR) of 75
mL/min/1.73 m [2]. However, this approach has been demonstrated to result in significant
misclassification [6] and should not be utilized.
2
The European Renal Best Practice (ERBP) group recommended that the first documented
serum creatinine be used as the baseline, rather than using historical values (ie, prior to the
acute illness) or a calculated value based on a presumed baseline GFR of 75 mL/min [6].
However, the initial hospital creatinine value may already be elevated above the patient's
usual baseline if the onset of AKI occurred prior to hospital admission. Creatinine
production may also be reduced in the setting of acute illness, leading to an artifactual fall

A more global concern raised by the Kidney Disease Outcomes Quality Initiative (KDOQI) work
group is that the use of a definition based upon a biomarker, such as serum creatinine, or a
variable, such as urine output, may result in a marked increase in the number of nephrology
consultations, which would provide uncertain benefit to the patient [7]. As noted by an
accompanying editorial to the KDOQI commentary, discretion is required to determine the
clinical significance of a diagnosis of AKI [18].
UTILITY IN EPIDEMIOLOGIC STUDIES
The Kidney Disease: Improving Global Outcomes (KDIGO) criteria have greatest utility in
epidemiologic studies and in defining consistent inclusion criteria and/or endpoints for clinical
studies [7,8]. The severity of AKI stage is correlated with mortality risk and intensive care unit
(ICU) and hospital length of stay [10,19-31].
It seems likely that these criteria will eventually be replaced, at least in part, by sensitive and
specific biomarkers of renal tubular injury. The use of such biomarkers, analogous to troponin
as a marker of myocardial injury, may allow development of a new classification of AKI that is
not solely dependent upon serum creatinine or other functional markers.
INFORMATION FOR PATIENTS
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics."
The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading
level, and they answer the four or five key questions a patient might have about a given
condition. These articles are best for patients who want a general overview and who prefer
short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more
sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading
in admission serum creatinine [15]. Changes in volume of distribution of creatinine as the
result of volume overload may also depress baseline creatinine values and blunt the rise in
creatinine concentration during AKI. Some experts have suggested that an average of
creatinine values measured 7 to 365 days prior to hospitalization best approximates the
true baseline creatinine value [16].
Even when a baseline creatinine is available, relying on small changes in serum creatinine
for the diagnosis of AKI may be associated with a high rate of misdiagnosis, especially in
patients with a baseline serum creatinine ≥1.5 mg/dL [17].
th th
th th

level and are best for patients who want in-depth information and are comfortable with some
medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print
or e-mail these topics to your patients. (You can also locate patient education articles on a
variety of subjects by searching on "patient info" and the keyword(s) of interest.)
SUMMARY
Basics topic (see "Patient education: Acute kidney injury (The Basics)")
●
Acute kidney injury (AKI) refers to the abrupt decrease in kidney function, resulting in the
retention of urea and other nitrogenous waste products and in the dysregulation of
extracellular volume and electrolytes. The term AKI has replaced acute renal failure (ARF),
reflecting the recognition that smaller decrements in kidney function are associated with
increased morbidity and mortality. (See 'Introduction' above.)
●
A consensus definition and criteria for AKI has been sequentially developed. The Kidney
Disease: Improving Global Outcomes (KDIGO) AKI Workgroup definition and staging system
is the preferred definition:
●
Increase in serum creatinine by ≥0.3 mg/dL (≥26.5 micromol/L) within 48 hours, or
•
Increase in serum creatinine to ≥1.5 times baseline, which is known or presumed to
have occurred within the prior seven days, or
•
Urine volume <0.5 mL/kg/hour for six hours
•
Using the KDIGO criteria, AKI is staged as follows:
●
Stage 1 – Increase in serum creatinine to 1.5 to 1.9 times baseline, or increase in serum
creatinine by ≥0.3 mg/dL (≥26.5 micromol/L), or reduction in urine output to <0.5
mL/kg/hour for 6 to 12 hours.
•
Stage 2 – Increase in serum creatinine to 2.0 to 2.9 times baseline, or reduction in urine
output to <0.5 mL/kg/hour for ≥12 hours.
•
Stage 3 – Increase in serum creatinine to 3.0 times baseline, or increase in serum
creatinine to ≥4.0 mg/dL (≥353.6 micromol/L), or reduction in urine output to <0.3
mL/kg/hour for ≥24 hours, or anuria for ≥12 hours, or the initiation of kidney
•

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REFERENCES
1. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl 2012; 2:8.
2. Bellomo R, Ronco C, Kellum JA, et al. Acute renal failure - definition, outcome measures,
animal models, fluid therapy and information technology needs: the Second International
Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care 2004;
8:R204.
3. Mehta RL, Kellum JA, Shah SV, et al. Acute Kidney Injury Network: report of an initiative to
improve outcomes in acute kidney injury. Crit Care 2007; 11:R31.
4. Levin A, Warnock DG, Mehta RL, et al. Improving outcomes from acute kidney injury: report
of an initiative. Am J Kidney Dis 2007; 50:1.
5. Molitoris BA, Levin A, Warnock DG, et al. Improving outcomes from acute kidney injury. J
Am Soc Nephrol 2007; 18:1992.
6. Ad-hoc working group of ERBP, Fliser D, Laville M, et al. A European Renal Best Practice
(ERBP) position statement on the Kidney Disease Improving Global Outcomes (KDIGO)
clinical practice guidelines on acute kidney injury: part 1: definitions, conservative
management and contrast-induced nephropathy. Nephrol Dial Transplant 2012; 27:4263.
7. Palevsky PM, Liu KD, Brophy PD, et al. KDOQI US commentary on the 2012 KDIGO clinical
practice guideline for acute kidney injury. Am J Kidney Dis 2013; 61:649.
8. James M, Bouchard J, Ho J, et al. Canadian Society of Nephrology commentary on the 2012
KDIGO clinical practice guideline for acute kidney injury. Am J Kidney Dis 2013; 61:673.
9. Barasch J, Zager R, Bonventre JV. Acute kidney injury: a problem of definition. Lancet 2017;
389:779.
10. Cruz DN, Bolgan I, Perazella MA, et al. North East Italian Prospective Hospital Renal
Outcome Survey on Acute Kidney Injury (NEiPHROS-AKI): targeting the problem with the
RIFLE Criteria. Clin J Am Soc Nephrol 2007; 2:418.
replacement therapy, or, in patients <18 years, decrease in estimated glomerular
filtration rate (eGFR) to <35 mL/min/1.73 m . (See 'Staging criteria' above.)
2
The AKI definition does not distinguish between the multiple etiologies that can cause AKI.
Other limitations include the use of urine output as a sole criterion for AKI, which has not
been conclusively validated, and difficulty determining baseline kidney function among
patients who have not had recent creatinine measurement. (See 'Limitations' above.)
●

11. Petäjä L, Vaara S, Liuhanen S, et al. Acute Kidney Injury After Cardiac Surgery by Complete
KDIGO Criteria Predicts Increased Mortality. J Cardiothorac Vasc Anesth 2016.
12. Qin JP, Yu XY, Qian CY, et al. Value of Kidney Disease Improving Global Outcomes Urine
Output Criteria in Critically Ill Patients: A Secondary Analysis of a Multicenter Prospective
Cohort Study. Chin Med J (Engl) 2016; 129:2050.
13. Claure-Del Granado R, Macedo E, Chertow GM, et al. Toward the optimal dose metric in
continuous renal replacement therapy. Int J Artif Organs 2012; 35:413.
14. Kellum JA, Sileanu FE, Murugan R, et al. Classifying AKI by Urine Output versus Serum
Creatinine Level. J Am Soc Nephrol 2015; 26:2231.
15. Prowle JR, Kolic I, Purdell-Lewis J, et al. Serum creatinine changes associated with critical
illness and detection of persistent renal dysfunction after AKI. Clin J Am Soc Nephrol 2014;
9:1015.
16. Siew ED, Ikizler TA, Matheny ME, et al. Estimating baseline kidney function in hospitalized
patients with impaired kidney function. Clin J Am Soc Nephrol 2012; 7:712.
17. Lin J, Fernandez H, Shashaty MG, et al. False-Positive Rate of AKI Using Consensus
Creatinine-Based Criteria. Clin J Am Soc Nephrol 2015; 10:1723.
18. Levey AS, Levin A, Kellum JA. Definition and classification of kidney diseases. Am J Kidney
Dis 2013; 61:686.
19. Ali T, Khan I, Simpson W, et al. Incidence and outcomes in acute kidney injury: a
comprehensive population-based study. J Am Soc Nephrol 2007; 18:1292.
20. Uchino S, Bellomo R, Goldsmith D, et al. An assessment of the RIFLE criteria for acute renal
failure in hospitalized patients. Crit Care Med 2006; 34:1913.
21. Hoste EA, Clermont G, Kersten A, et al. RIFLE criteria for acute kidney injury are associated
with hospital mortality in critically ill patients: a cohort analysis. Crit Care 2006; 10:R73.
22. Kuitunen A, Vento A, Suojaranta-Ylinen R, Pettilä V. Acute renal failure after cardiac surgery:
evaluation of the RIFLE classification. Ann Thorac Surg 2006; 81:542.
23. Ostermann M, Chang RW. Acute kidney injury in the intensive care unit according to RIFLE.
Crit Care Med 2007; 35:1837.
24. Ricci Z, Cruz D, Ronco C. The RIFLE criteria and mortality in acute kidney injury: A systematic
review. Kidney Int 2008; 73:538.
25. Bagshaw SM, George C, Dinu I, Bellomo R. A multi-centre evaluation of the RIFLE criteria for
early acute kidney injury in critically ill patients. Nephrol Dial Transplant 2008; 23:1203.
26. Thakar CV, Christianson A, Freyberg R, et al. Incidence and outcomes of acute kidney injury
in intensive care units: a Veterans Administration study. Crit Care Med 2009; 37:2552.

27. Joannidis M, Metnitz B, Bauer P, et al. Acute kidney injury in critically ill patients classified by
AKIN versus RIFLE using the SAPS 3 database. Intensive Care Med 2009; 35:1692.
28. Teles F, de Mendonça Uchôa JV, Mirelli Barreto Mendonça D, Falcão Pedrosa Costa A. Acute
kidney injury in leptospirosis: the Kidney Disease Improving Global Outcomes (KDIGO)
criteria and mortality . Clin Nephrol 2016; 86 (2016):303.
29. Bıyık M, Ataseven H, Bıyık Z, et al. KDIGO (Kidney Disease: Improving Global Outcomes)
criteria as a predictor of hospital mortality in cirrhotic patients. Turk J Gastroenterol 2016;
27:173.
30. Hoste EA, Bagshaw SM, Bellomo R, et al. Epidemiology of acute kidney injury in critically ill
patients: the multinational AKI-EPI study. Intensive Care Med 2015; 41:1411.
31. Coca SG, King JT Jr, Rosenthal RA, et al. The duration of postoperative acute kidney injury is
an additional parameter predicting long-term survival in diabetic veterans. Kidney Int 2010;
78:926.
Topic 7238 Version 30.0

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GRAPHICS
Criteria for acute kidney injury
RIFLE AKIN KDIGO
Diagnostic criteria*
Increase in serum creatinine
of ≥0.3 mg/dL or ≥50% within
48 hours
OR
Urine output of <0.5
mL/kg/hour for >6 hours
of ≥0.3 mg/dL within 48 hours
or ≥50% within 7 days
OR
mL/kg/hour for >6 hours
Staging criteria
Risk (RIFLE) or stage 1
(AKIN/KDIGO)
to 1.5 times baseline
OR
mL/kg/hour for 6 to 12 hours
of ≥0.3 mg/dL or to 150 to
200% baseline
OR
of ≥0.3 mg/dL or 1.5 to 1.9
times baseline
OR
Injury (RIFLE) or stage 2
(AKIN/KDIGO)
of to 2 times baseline
OR
to 200 to 300% baseline
OR
to 2.0 to 2.9 times baseline
OR
Failure (RIFLE) or stage 3
(AKIN/KDIGO)
to 3 times baseline
OR
by >0.5 mg/dL to >4.0 mg/dL
OR
mL/kg/hour for >24 hours or
anuria for >12 hours
OR
Initiation of renal replacement
therapy
Increase in serum
creatinine to >300% baseline
OR
by >0.5 mg/dL to ≥4.0 mg/dL
OR
mL/kg/hour for >24 hours or
anuria for >12 hours
OR
therapy
Increase in serum
creatinine to ≥3.0 times
baseline
OR
of ≥0.3 mg/dL to ≥4.0 mg/dL
OR
mL/kg/hour for ≥24 hours or
anuria for ≥12 hours
OR
therapy
Loss (RIFLE) Need for renal replacement
therapy for >4 weeks

End stage (RIFLE) Need for renal replacement
therapy for >3 months

RIFLE: risk, injury, failure, loss, ESRD; AKIN: Acute Kidney Injury Network; KDIGO: Kidney Disease: Improving Global Outcomes; ESRD:
end-stage renal disease.
* AKIN and KDIGO provided both diagnostic and staging criteria. RIFLE provided a graded definition of AKI that is implicit in the staging
criteria.
¶ In patients <18 years, stage 3 AKI is also defined by KDIGO as a decrease in estimated glomerular filtration rate (eGFR) to <35
mL/min/1.73 m .
References:
1. Bellomo R, Ronco C, Kellum JA, et al. Acute renal failure-definition, outcome measures, animal models, fluid therapy and information
technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care 2004;
[1] [2] [3]
¶
2

8:B204. Copyright © 2004 BioMed Central Ltd.
2. Mehta RL, Kellum JA, Shah SV, et al. Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury. Crit
Care 2007; 11:R31. Copyright © 2007 BioMed Central Ltd.
3. Kidney Disease: Improving Global Outcomes (KDIGO). Acute Kidney Injury Work Group. KDIGO clinical practice guidelines for acute kidney
injury. Kidney Int Suppl 2012; 2:1.
Graphic 83168 Version 12.0

Contributor Disclosures
Paul M Palevsky, MD Grant/Research/Clinical Trial Support: Dascena [Informatics; prediction of
AKI]. Gary C Curhan, MD, ScD Employment: OM1, Inc [Healthcare data analytics company] - No relevant
conflict on topic. Equity Ownership/Stock Options: Allena Pharmaceuticals; OM1, Inc. Consultant/Advisory
Boards: Allena Pharmaceuticals [Oxalate, nephrolithiasis]; Decibel Therapeutics [Hearing loss/tinnitus];
Shire [Hypoparathyroidism]; AstraZeneca [Hyperkalemia]; OM1, Inc [Nephrology]; Orfan [Hyperoxaluria];
Dicerna [Hyperoxaluria]. Consultant/Advisory Boards (spouse/partner): Decibel Therapeutics [Hearing loss,
tinnitus]. Shveta Motwani, MD, MMSc, FASN Nothing to disclose
Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are
addressed by vetting through a multi-level review process, and through requirements for references to be
provided to support the content. Appropriately referenced content is required of all authors and must
conform to UpToDate standards of evidence.
Conflict of interest policy
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