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Are eGFR equations better than IDMS-traceable serum creatinine in classifying chronic kidney disease?

Abstract Objective: In 2002, a uniform definition of chronic kidney disease (CKD) became widely accepted. The level of glomerular filtration rate (GFR) is the pivot for staging the disease. Because GFR is not readily measured in routine clinical practice, statistical models such as the Modification of Diet in Renal Disease (MDRD) equation have been proposed for estimating GFR. The MDRD equation is gaining worldwide acceptance in assisting the diagnosis and staging of CKD. Material and methods: We use theoretical and experimental considerations based on serum creatinine (Scr) measurements obtained with an enzymatic IDMS-traceable assay and compare CKD classifications based on Scr alone with classifications based on the eGFR-MDRD and eGFR-Mayo Clinic equations. Results: Based on recently published reference intervals for enzymatically determined Scr, we show that eGFR-MDRD<60 mL/min/1.73m2 corresponds extremely well with Scr>upper reference limit. The different CKD stages III, IV and V can be redefined using Scr alone, resulting in 97.5% agreement. Conclusion: We show that neither the MDRD study equation nor the Mayo Clinic equation add extra value to the information already contained in Scr itself. Because of the limited applicability of the eGFR equations, Scr has even more potential to assist in the diagnosis and classification of CKD than eGFR-MDRD.