Validation of Equations to Estimate Glomerular Filtration Rate in South Africans of Mixed Ancestry

Background: The Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations are two commonly used formulae to estimate glomerular filtration rate (GFR) in adults. The CKD-EPI equation is recommended in current international and local guidelines for the diagnosis and management of chronic kidney disease (CKD), unless an alternative equation has been shown to have superior accuracy. Validation and comparison of the equations in local populations are therefore required. Previous studies have reported on the accuracy of these prediction equations in black South Africans and those of Indian ancestry.

Objectives: To evaluate the MDRD and CKD-EPI equations in South African (SA) adults of mixed ancestry.

Methods: In all participants, GFR was measured (mGFR) from plasma clearance of 99mTc-diethylenetetraaminepenta-acetic acid (99mTc-DTPA), using a standardised technique. Serum creatinine assays were isotope dilution mass spectrometry traceable. GFR was estimated (eGFR) using the MDRD and CKD-EPI equations, with and without the black ethnicity factor. The agreement, bias, precision and accuracy of each equation was determined.

Results: Eighty adults were included (30 male, median age 39 years, median GFR 59 mL/min/1.73 m2). Sixty-eight had a diagnosis of CKD, 10 were potential kidney donors, and 2 were healthy volunteers. Both equations, without the black ethnicity factor, had good agreement with measured GFR. The equations tended to overestimate GFR, with bias of 1.6 and 7.9 mL/min/1.73 m2 for the MDRD and CKD-EPI equations, respectively. The interquartile ranges of the differences were 15.9 and 20.2 mL/min/1.73 m2, and as a measure of accuracy, the percentages of estimates that fell within 30% of the mGFR (P30) were 80% and 72.5% (p=0.18). For identification of individuals with a GFR <60 mL/min/1.73 m2, the sensitivity of MDRD eGFR was 97.3% and that of CKD-EPI eGFR was 97.1%.

Conclusions: The MDRD and CKD-EPI equations have shown satisfactory and comparable performance in this SA mixed-ancestry adult population, with the MDRD equation marginally less biased than the CKD-EPI.