Estimating Glomerular Filtration Rate in Black South Africans by Use of the Modification of Diet in Renal Disease and Cockcroft-Gault Equations

Abstract

Background: The 4-variable Modification of Diet in Renal Disease (4-v MDRD) and Cockcroft-Gault (CG) equations are commonly used for estimating glomerular filtration rate (GFR); however, neither of these equations has been validated in an indigenous African population. The aim of this study was to evaluate the performance of the 4-v MDRD and CG equations for estimating GFR in black South Africans against measured GFR and to assess the appropriateness for the local population of the ethnicity factor established for African Americans in the 4-v MDRD equation. Methods: We enrolled 100 patients in the study. The plasma clearance of chromium-51–EDTA (51Cr-EDTA) was used to measure GFR, and serum creatinine was measured using an isotope dilution mass spectrometry (IDMS) traceable assay. We estimated GFR using both the reexpressed 4-v MDRD and CG equations and compared it to measured GFR using 4 modalities: correlation coefficient, weighted Deming regression analysis, percentage bias, and proportion of estimated GFR within 30% of measured GFR (P30). Results: The Spearman correlation coefficient between measured and estimated GFR for both equations was similar (4-v MDRD R2 = 0.80 and CG R2 = 0.79). Using the 4-v MDRD equation with the ethnicity factor of 1.212 as established for African Americans resulted in a median positive bias of 13.1 (95% CI 5.5 to 18.3) mL/min/1.73 m2. Without the ethnicity factor, median bias was 1.9 (95% CI −0.8 to 4.5) mL/min/1.73 m2. Conclusions: The 4-v MDRD equation, without the ethnicity factor of 1.212, can be used for estimating GFR in black South Africans.

Prevalence of Chronic Kidney Disease in Hypertensive Patients in Ghana

“…The MDRD equation has, however, been validated in South African blacks and the four-variable MDRD equation without the ethnicity factor of 1.212 accurately reflected isotopic GFR. 21 If we followed this conclusion, this would increase the prevalence of CKD. With these provisos, we report a high prevalence of CKD in hypertensive patients in Ghana.…”

Are the Creatinine-Based Equations Accurate to Estimate Glomerular Filtration Rate in African American Populations?

“…This is the case for the well known Cockcroft and Gault equation (3,7,(13)(14)(15). In 1999, the Modification of Diet in Renal Disease (MDRD) study equation has been published and an ethnic correction factor has been proposed for African Americans (8).…”

“…However, this a priori surprising result could also be explained, at least in part, by the low socioeconomic level in black South Africans and the high percentage of HIV patients (20%) included in the South African trial. Both conditions will probably negatively influence the muscular mass, especially when compared to African Americans, thus leading to GFR overestimation by the MDRD study equation (14). This is also indirectly suggested by the difference in weight observed between the trials (mean weight of 69.5 kg in South Africans versus 84.1 kg in African Americans in the MDRD study) (8,14).…”

“…The study published in 2008 by van Deventer et al is of interest because they have analyzed 100 black South African people (14). For the first (and only) time, performance of the (four-variable) MDRD study equation was evaluated against a GFR reference method in African non-American people.…”

“…Both conditions will probably negatively influence the muscular mass, especially when compared to African Americans, thus leading to GFR overestimation by the MDRD study equation (14). This is also indirectly suggested by the difference in weight observed between the trials (mean weight of 69.5 kg in South Africans versus 84.1 kg in African Americans in the MDRD study) (8,14). The same results have also been found in Ghanaian populations even if GFR was only estimated by creatinine clearance (and not measured GFR) (11).…”