Polar Views in Nephrology Pro : Estimating GFR using the chronic kidney disease epidemiology collaboration ( CKD-EPI ) 2009 creatinine equation : the time for change is now

Clinical assessment of kidney function is central to the practice of medicine. Glomerular filtration rate (GFR) is widely accepted as the best index of kidney function in health and disease and accurate values are required for optimal decisionmaking in many clinical settings. GFR is generally not measured in clinical practice, but is estimated from the serum level of an endogenous filtration marker. GFR-estimating equations are useful because they provide a more accurate estimate of measured GFR than the serum level of the filtration marker alone, and they are expressed in the same units as measured GFR, which facilitates clinical decisions based on the level of kidney function. Serum creatinine is ordered to estimate the GFR more than 281 million times annually in the USA [1], and recent reports show that more than 80% of US clinical laboratories now report estimated GFR (eGFR) whenever serum creatinine is ordered [2]. Worldwide estimates are not known, but eGFR is routinely reported in the UK, France and Australia. The majority of laboratories report eGFR using the Modification of Diet in Renal Disease (MDRD) study equation. However, an increasing number of laboratories are now beginning to use the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 creatinine equation [3, 4] (Olivier Allaire, personal communication), which uses the same variables as the MDRD study but is more accurate across the range of GFR [1, 5, 6]. Widespread implementation of GFR estimation would be facilitated by the use of a single equation expressed for the use with standardized creatinine that is accurate over the full range of GFR and applicable throughout the world. Three years have passed since we first reported the development and validation of the CKD-EPI creatinine equation and proposed that it replace the MDRD study equation for routine eGFR reporting [5]. At that time, there were some who resisted this change, arguing that further validation was needed, that the improvement in accuracy was small, and that there would likely be a newer equation later, so why change now? It is now apparent from an extensive body of literature that the CKDEPI equation provides a more accurate estimate of measured GFR, it provides a better tool for clinical practice, research and public health, no other widely applicable creatinine-based estimating equation is more accurate, and we are not aware of ongoing efforts to develop an alternative creatinine-based equation for widespread application. In this editorial, we briefly review the physiologic and statistical basis for development and validation of GFR-estimating equations and the literature comparing the MDRD study and CKD-EPI equations for estimating measured GFR, detecting chronic kidney disease (CKD), estimating CKD prevalence and prognosis and guiding therapy. We conclude with considerations for implementing the change from the MDRD study equation to the CKD-EPI equation for reporting eGFR by clinical laboratories. In our opinion, it is clear that the time for change is now.