Estimating Equations for Glomerular Filtration Rate in the Era of Creatinine Standardization

Abstract

BACKGROUND: Clinical laboratories are increasingly reporting estimated glomerular filtration rate (GFR) by using serum creatinine assays traceable to a standard reference material. PURPOSE: To review the performance of GFR estimating equations to inform the selection of a single equation by laboratories and the interpretation of estimated GFR by clinicians. DATA SOURCES: A systematic search of MEDLINE, without language restriction, between 1999 and 21 October 2011. STUDY SELECTION: Cross-sectional studies in adults that compared the performance of 2 or more creatinine-based GFR estimating equations with a reference GFR measurement. Eligible equations were derived or reexpressed and validated by using creatinine measurements traceable to the standard reference material. DATA EXTRACTION: Reviewers extracted data on study population characteristics, measured GFR, creatinine assay, and equation performance. DATA SYNTHESIS: Eligible studies compared the MDRD (Modification of Diet in Renal Disease) Study and CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations or modifications thereof. In 12 studies in North America, Europe, and Australia, the CKD-EPI equation performed better at higher GFRs (approximately >60 mL/min per 1.73 m(2)) and the MDRD Study equation performed better at lower GFRs. In 5 of 8 studies in Asia and Africa, the equations were modified to improve their performance by adding a coefficient derived in the local population or removing a coefficient. LIMITATION: Methods of GFR measurement and study populations were heterogeneous. CONCLUSION: Neither the CKD-EPI nor the MDRD Study equation is optimal for all populations and GFR ranges. Using a single equation for reporting requires a tradeoff to optimize performance at either higher or lower GFR ranges. A general practice and public health perspective favors the CKD-EPI equation. PRIMARY FUNDING SOURCE: Kidney Disease: Improving Global Outcomes.