The KDIGO classification system

The KDIGO has not been the focus of any CICM exam questions.

It was first published as a guidelines statement in 2012. It is essentially a combined RIFLE/AKIN system, incorporating the better elements of both, and thus unfortunately also retaining their defects.

A lukewarm response from the Americans published in 2013 serves as an excellent summary of the KDIGO recommendation statements, and a source for much of the critiques.

The Recommendations

The abovementioned American Response has within it a handy summary box (Box 1, p.653).

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 × 2.0-2.9 (i.e. doubled or tripled creatinine)	u/o < 0.5ml/kg/hr × more than 12 hrs
3	Creatinine × 3.0 OR: An increase up to a creatinine of 354 μmol/L or more OR: The initiation of RRT OR In patients <18 years, decrease in eGFR to <35 ml/min	u/o < 0.3ml/kg/hr × 24 hrs OR: Anuria for 12 hours

One might say that this is damn near identical to the AKIN classifications.

That is indeed accurate.

The definition of AKI in general is only slightly different.

• One now has 7 whole days to reach the 50% increase in creatinine, but only 48 hours to get an "absolute" increase of 26.4μmol/L.
• Stage 3 no longer requires a 44μmol/L increase in serum creatinine - rather, it expects that this level be reached within 48 hours (i.e. your creatinine rises from another more normal level.

Advantages over the AKIN and RIFLE classification:

Lopes et al have published "a critical and comprehensive review" of the RIFLE and AKIN criteria in 2012. This summary owes much to their article.

 

Advantages of the KDIGO system over the AKIN and RIFLE systems:

• A unified system is important to maintain the international coherence of research.Generally speaking, we should all agree on one system of classification, and then agree to use it for all our research.

• One has the freedom to use baseline creatinine if it is available; but it is by no means essential (two measurements within the same 48 hour period could be performed, and the baseline creatinine value can be replaced by the first "reference" reading).

• The KDIGO classification could theoretically improve the AKIN criteria sensitivity; by broadening the definition of AKI, it will detect more patients with AKI, and inadvertantly pick up a number of patients who look like AKI but whose kidneys are intact.

Criticisms of the KDIGO system:

• The unification of classification systems only works if everybody is in agreement. The Americans in fact only agreed to use this system of classification for epidemiology studies. However, they also concluded that it has not been sufficiently validated to direct therapy.

• The broadening of the definitions leads to an inefficient use of healthcare resources: The Americans objected that too many people would meet AKI criteria, and too many nephrology referrals would be generated by the increasingly defensive American health system.

• There is still no role played by duration of AKI in the staging scales. The duration of AKI plays a major role in prognosis - the longer you spend in renal failure, the worse your overall risk of all-causes mortality.