What Is the Most Appropriate Formula to Use in Estimating Glomerular Filtration Rate in Adult Arabs without Kidney Disease?

Abstract

Background. In clinical practice, the glomerular filtration rate (GFR) is often estimated by the Modification of Diet in Renal Disease (MDRD) or Cockcroft-Gault (CG) formulae. No data are available, however, on the performance of these formulae in Arab individuals. Methods. Plasma creatinine samples were obtained from 90 consecutive normal Arab kidney donors for the estimation of GFR (eGFR) using the simplified MDRD and CG formulae. The GFR was measured in these donors with chromium labelled EDTA {[51Cr] EDTA). Bias was assessed by calculating the difference between the measured GFR and the calculated GFR using each of the two formulae; precision was calculated using the r value of the regression analysis. Results. The group studied consisted of 90 donors, of whom 64 were males (71%). The mean age was 30.8 years (± 9.8) and mean BMI was 25.7 (± 5.7). The measured GFR (mean 112.4 ± 17.5) correlated better with the calculated GFR by CG formula (mean 107.7 ± 29.7) and showed poor correlation with the GFR estimated by the MDRD (mean 89.2 ± 13.8); bias = 4.8 and 23.3, respectively (p = 0.1 and < 0.0001, respectively). The correlation with CG formula was better in males (bias = 2, p = 0.5) and those under 30 years of age (bias = 1.0, p = 0.9). Based on our data, we calculated a correction factor to the CG formula to improve the correlation with the measured GFR in Arab individuals. By multiplying the CG formula by 1.0446, the bias was reduced from 4.8 (p = 0.1) to 0.0 (p = 0.5) with an increase in precision from 0.2 (p = 0.05) to 0.43 (p = 0.0001). Using CG formula, the frequency for values within 30% of the mean of the measured value was 75%, which improved to 80% using the revised formula. Conclusions. CG formula was found to be the most appropriate for calculation of GFR in Arab individuals. It is possible to reduce the bias and improve precision in Arab individuals with normal renal function by multiplying the result obtained by CG formula by 1.0446.