Relative performance of the MDRD and CKD-EPI equations for estimating glomerular filtration rate among patients with varied clinical presentations

Abstract

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 underwent 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 presentation. 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 equation had higher specificity than the MDRD equation for detecting an mGFR <60 ml/min per 1.73 m(2) (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.

Figure 1.

GFR measured by iothalamate clearance (mGFR) is plotted against GFR estimated by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation (Panel A) and the Modification of Diet in Renal Disease (MDRD) equation (Panel B) on a log-log scale for 5238 patients. The black dashed line represents the line of identity. With either equation, the blue regression line for potential kidney donors (blue ×) and the red regression line for postnephrectomy kidney donors (red □) show systematic deviation (underestimation) from the line of identity. With the CKD-EPI equation, the black solid regression line for native CKD and transplant recipients (black dots) also shows systemic deviation (overestimation) from the line of identity.

Figure 2.

Bias with estimated GFR (eGFR) by age (years). Mean percentage bias (eGFR − mGFR)/mGFR (Panel A) and mean bias calculated for log eGFR − log mGFR (Panel B) are both depicted. The CKD-EPI equation is represented by the solid smoother curves (lambda = 1000,000), and the MDRD equation is represented by the dashed smoother curves. Native CKD and transplant recipients (n = 4558) are represented by the black curves, and the potential kidney donors and postnephrectomy kidney donors (n = 680) are represented by the gray curves.