A comparison of classification systems for acute kidney injury

By Alex Yartsev - Jul 12, 2015
Last updated Sun, 11/01/2015 - 01:32
 Topic: Renal Failure and Dialysis

Prior to the RIFLE criteria, there were about thirty different classification systems. This brief summary chapter focuses only on the RIFLE, AKIN and KDIGO systems. A tabulated summary of their advantages and disadvantages offers a means of rapid revision.

A Comparison of Acute Kidney Injury Classification Systems

RIFLE classification
 

Publication:

Ronco Bellomo and Kellum ( 2004):
 

Basis:

Category

 GFR criteria Urine output criteria

Risk

 Creatinine × 1.5 u/o < 0.5ml/kg/hr × 6 hrs

Injury

 Creatinine × 2 u/o < 0.5ml/kg/hr × 12 hrs

Failure

 Creatinine × 3 u/o < 0.3ml/kg/hr × 24 hrs

Loss

 Complete loss of function > 4 weeks  

End-stage

 Complete loss of function > 3 months  
 

Advantages:
  • Validated as a means of prognostic stratification of acute kidney injury.
  • It is successful as a definition and stratification of AKI severity.
 

Criticism:
  • Not predictive: classifies AKI only after it is established.
  • The urine and creatinine criteria are unbalanced - different outcomes occur within the same class, depending on which parameter was measured
  • Urine criteria rely on impractical measurements.
  • Urine output criteria are altered by diuretics, DI, etc..
  • Urine output measurements may be inaccurate.
  • The criteria for creatinine rely on the availability of baseline values, which are rarely available.
  • Nobody seems to agree on what the definiton of "baseline" creatinine is.
  • Creatinine levels may be affected by factors which do not affect outcome.
  • The rate of creatinine rise is unaccounted for.
  • The "Risk" criteria for creatinine may not be sensitive enough.
  • The criteria require true GFR, rather than an estimated GFR.
  • The criteria make no attempt to distinguish between different aetiologies.

AKIN classification
 

Publication:

Mehta, Kellum et al (2007)
 

Basis:

Stage

Serum creatinine Urine output criteria

1

 Creatinine × 1.5 - 2.0 from baseline
OR:
Creatinine increased by at least 26.4μmol/L		 u/o < 0.5ml/kg/hr × 6 hours

2

 Creatinine × 2.0-3.0 (i.e. doubled or tripled creatinine) u/o < 0.5ml/kg/hr × 12 hrs

3

 Creatinine × 2.0-3.0
OR:
A creatinine over 354 μmol/L, with an acute increase by at least 44 μmol/L		 u/o < 0.3ml/kg/hr × 24 hrs
OR:
Anuria for 12 hours
 

Improvements:
  • The AKIN score is independently associated with outcome. (Just as RIFLE is)
  • The score is taken after hypovolemia has been corrected, thus excluding a group who were merely dehydrated.
  • The score demands that urinary tract obstruction is excluded.
  • The GFR is discarded, killing the controversy of how one should measure it.
  • Baseline creatinine is not required (though two measurements within the same 48 hour period are necessary).
  • There is a defined timeframe over which the creatinine is measured, this being 48 hours.
  • A small absolute increase in creatinine will still be detected as "Stage 1"
  • The AKIN classification could theoretically improve the RIFLE criteria sensitivity and specificity.
 

Criticism:
  • Creatinine has to be measured within a 48 hour window, which may exclude more slowly progressive aetiologies.
  • Patients who are subjected to RRT are scored as Stage 3, irrespective of the indication for RRT
  • There is a significant variability in local practice regarding commencement of RRT.
  • Patients are scored only after an "optimal state of hydration" is achieved, but this is an ill-defined state.
  • There is no difference in predictive acuity between these two systems. Use either one; who cares. Whatever.

KDIGO classification
 

Publication:

KDIGO Clinical Practice Guidelines (2012)
 

Basis:

A combination of the RIFLE and AKIN:

Stage

Serum creatinine criteria Urine output criteria

1

 Creatinine × 1.5 - 1.9 from baseline over 7 days
OR:
Creatinine increased by at least 26.4μmol/L over 48 hrs		 u/o < 0.5ml/kg/hr × 6-12 hours

2

 Creatinine × 2.0-3.0 (i.e. doubled or tripled creatinine) u/o < 0.5ml/kg/hr × more than 12 hrs

3

 Creatinine × 2.0-3.0
OR:
An increase up to a creatinine of 354 μmol/L or more
OR:
The initiation of RRT		 u/o < 0.3ml/kg/hr × 24 hrs
OR:
Anuria for 12 hours
 

Improvements:
  • A unified system is important to maintain the international coherence of research.
  • One has the freedom to use baseline creatinine if it is available; but it is by no means essential
  • The KDIGO classification could theoretically improve the AKIN criteria sensitivity;
 

Criticism:
  • The unification of classification systems only works if everybody is in agreement.
  • The broadening of the definitions leads to an inefficient use of healthcare resources.
  • There is still no role played by duration of AKI in the staging scales.

References

Bellomo, Rinaldo, 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." Critical care 8.4 (2004): R204.

Cruz, Dinna N., Zaccaria Ricci, and Claudio Ronco. "Clinical review: RIFLE and AKIN–time for reappraisal." Critical care 13.3 (2009): 211.

Hoste, Eric AJ, and John A. Kellum. "Acute kidney injury: epidemiology and diagnostic criteria." Current opinion in critical care 12.6 (2006): 531-537.

Chertow, Glenn M., et al. "Acute kidney injury, mortality, length of stay, and costs in hospitalized patients." Journal of the American Society of Nephrology16.11 (2005): 3365-3370.

Lopes, José António, and Sofia Jorge. "The RIFLE and AKIN classifications for acute kidney injury: a critical and comprehensive review." Clinical Kidney Journal 6.1 (2013): 8-14.

Mehta, Ravindra L., et al. "Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury." Critical care 11.2 (2007): R31.

Fliser, Danilo, 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." Nephrology Dialysis Transplantation (2012): gfs375.

Palevsky, Paul M., et al. "KDOQI US commentary on the 2012 KDIGO clinical practice guideline for acute kidney injury." American Journal of Kidney Diseases 61.5 (2013): 649-672.

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