Assessment of GFR by four methods in adults in Ashanti, Ghana: the need for an eGFR equation for lean African populations

BACKGROUND Equations for estimating glomerular filtration rate (GFR) have not been validated in Sub-Saharan African populations, and data on GFR are few. METHODS GFR by creatinine clearance (Ccr) using 24-hour urine collections and estimated GFR (eGFR) using the four-variable Modification of Diet in Renal Disease (MDRD-4)[creatinine calibrated to isotope dilution mass spectrometry (IDMS) standard], Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Cockcroft-Gault equations were obtained in Ghanaians aged 40-75. The population comprised 1013 inhabitants in 12 villages; 944 provided a serum creatinine and two 24-hour urines. The mean weight was 54.4 kg; mean body mass index was 21.1 kg/m(2). RESULTS Mean GFR by Ccr was 84.1 ml/min/1.73 m(2); 86.8% of participants had a GFR of >/=60 ml/min/1.73 m(2). Mean MDRD-4 eGFR was 102.3 ml/min/1.73 m(2) (difference vs. Ccr, 18.2: 95% CI: 16.8-19.5); when the factor for black race was omitted, the value (mean 84.6 ml/min/1.73 m(2)) was close to Ccr. Mean CKD-EPI eGFR was 103.1 ml/min/1.73 m(2), and 89.4 ml/min/1.73 m(2) when the factor for race was omitted. The Cockcroft-Gault equation underestimated GFR compared with Ccr by 9.4 ml/min/1.73 m(2) (CI: 8.3-10.6); particularly in older age groups. GFR by Ccr, and eGFR by MDRD-4, CKD-EPI and Cockcroft-Gault showed falls with age: MDRD-4 5.5, Ccr 7.7, CKD-EPI 8.8 and Cockcroft-Gault 11.0 ml/min/1.73 m(2)/10 years. The percentage of individuals identified with CKD stages 3-5 depended on the method used: MDRD-4 1.6% (7.2 % without factor for black race; CKD-EPI 1.7% (4.7% without factor for black race), Ccr 13.2% and Cockcroft-Gault 21.0%. CONCLUSIONS Mean eGFR by both MDRD-4 and CKD-EPI was considerably higher than GFR by Ccr and Cockcroft-Gault, a difference that may be attributable to leanness. MDRD-4 appeared to underestimate the fall in GFR with age compared with the three other measurements; the fall with CKD-EPI without the adjustment for race was the closest to that of Ccr. An equation tailored specifically to the needs of the lean populations of Africa is urgently needed. For the present, the CKD-EPI equation without the adjustment for black race appears to be the most useful.