A review of studies comparing different creatinine-based glomerular filtration rate (GFR) estimating equations has been published early online in the Annals of Internal Medicine.

The authors note that accurate estimation of GFR is essential for detecting and staging chronic kidney disease (CKD), determining drug doses, and stratifying risk.  The most frequently used GFR equation is that derived from the MDRD (Modification of Diet in Renal Disease) Study; however this is known to be less accurate at higher GFRs and in racial and ethnic groups outside of North America, Europe, and Australia.  Other equations have therefore been developed and validated to overcome these limitations.

The purpose of their study was to review the performance of creatinine-based GFR estimation equations, used with standardised serum creatinine measurements, to inform the selection of a single equation that laboratories can use to estimate GFR.  They conducted a systematic search of MEDLINE from 1999 (the year before the MDRD Study equation was published) to 2011, looking for cross-sectional studies in adults comparing the performance of 2 or more creatinine-based GFR estimating equations with a reference GFR measurement. Eligible equations were derived or re-expressed and validated by using creatinine measurements traceable to a standard reference material.

The main findings were as follows:

• A total of 12 studies (n=12,898) conducted in North America, Europe, and Australia met their criteria and were included in the analysis.  All of these compared the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation with the MDRD Study equation.

• The CKD-EPI equation performed better at higher GFRs (approximately >60 mL/min per 1.73 m2) and the MDRD Study equation performed better at lower GFRs.

• A total of 8 studies conducted in populations outside of North America, Europe and Australia met the inclusion criteria; all were based in Asia or Africa.  The majority of studies involved locally modified equations and therefore the comparison of performance was limited.

• In 3 studies that compared the CKD-EPI and MDRD Study equations (with or without modification), the CKD-EPI equation was more accurate

The authors discuss the limitations of their research and summarise that neither the CKD-EPI nor the MDRD Study equation is optimal across all populations and GFR ranges, but that a general practice and public health perspective favours the CKD-EPI equation in North America, Europe, and Australia.