Con: Should we abandon the use of the MDRD equation in favour of the CKD-EPI equation?

The best overall index of renal function is the glomerular filtration rate (GFR) [1]. Since measuring the GFR can be cumbersome and costly, estimation of GFR is essential for the diagnosis and evaluation of chronic kidney disease (CKD), defined as kidney damage or GFR <60 niL/min/1.73 m 2 for ≥3 months and staged by levels of GFR according to the NKF KDOQI (The National Kidney Foundation Kidney Disease Outcomes Quality Initiative) guidelines published in 2002 [2]. These now decade-old guidelines are under consideration for revision by the KDIGO (Kidney Disease: Improving Global Outcomes) CKD Work Group [3]. Several authors have proposed in the past different equations to estimate GFR based on serum creatinine concentration, the latter being determined by the individual's muscular mass in steady state, and thus by age, gender and ethnicity [4-8]. Among these equations, the one proposed by Cockcroft and Gault in 1976 [4] was doubtless the most popular for many years because of its simplicity and ease to calculate at the patient's bedside. However, this equation is an estimation of the creatinine clearance, not of the GFR, and was particularly imprecise, notably in CKD patients. In 1999, an equation derived from measured GFR (mGFR) was developed in the Modification of Diet in Renal Disease (MDRD) Study. This equation included the serum creatinine concentration and six other variables, subsequently abbreviated to four variables [5, 6]. This equation has been endorsed by the KDOQI guidelines and is currently used by most clinical laboratories [2]. Several limitations of the MDRD study equation were elaborated on in the literature [9-12], the major one being the systematic underestimation of mGFR >60 mL/min/1.73 m 2 , which essentially translates in to overestimation of the CKD prevalence. A new equation, the CKD-Epidemiology Collaboration (CKD-EPI) equation, was proposed in 2009 for better estimation of GFR levels >60 mL/min/1.73 m 2 [7].