Summary Background The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was developed

using both CKD and non-CKD patients to potentially replace the Modification of Diet in Renal Disease (MDRD) equation that was derived with only CKD patients. The objective of our study was to compare the accuracy of the MDRD and CKD-EPI equations for estimating GFR in a large group of patients having GFR measurements for diverse clinical indications. Design, setting, participants, and measurements A cross-sectional study was conducted of patients who un-derwent renal function assessment for clinical purposes by simultaneous measurements of serum creatinine and estimation of GFR using the MDRD and CKD-EPI equations and renal clearance of iothalamate (n 5238). Results Bias compared with measured GFR (mGFR) varied for each equation depending on clinical presen-tation. The CKD-EPI equation demonstrated less bias than the MDRD equation in potential kidney donors (8 % versus 18%) and postnephrectomy donors (7 % versus 15%). However, the CKD-EPI equation was slightly more biased than the MDRD equation in native CKD patients (6 % versus 3%), kidney recipients (8% versus 1%), and other organ recipients (9 % versus 3%). Among potential kidney donors, the CKD-EPI equa-tion had higher specificity than the MDRD equation for detecting an mGFR 60 ml/min per 1.73 m2 (98% versus 94%) but lower sensitivity (50 % versus 70%). Conclusions Clinical presentation influences the estimation of GFR from serum creatinine, and neither the CKD-EPI nor MDRD equation account for this. Use of the CKD-EPI equation misclassifies fewer low-risk patients as having reduced mGFR, although it is also less sensitive for detecting mGFR below specific threshold values used to define CKD stages