Received on October 29, 2007
Accepted on April 7, 2008

General Clinical Chemistry

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

¹ Department of Chemical Pathology and NHLS, University of the Witwatersrand, Johannesburg, South Africa
² Biostatistics Unit, South African Medical Research Council and School of Therapeutic Sciences, University of the Witwatersrand, South Africa
³ Division of Nephrology, Chris Hani Baragwanath Hospital, University of the Witwatersrand, Johannesburg, South Africa

^* To whom correspondence should be addressed. E-mail: manuel.vandeventer{at}gmail.com.

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. We used plasma clearance of ⁵¹Cr-EDTA to measure GFR, and we measured serum creatinine 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 5.5–18.3) 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.