Estimating renal function in lupus nephritis: comparison of the Modification of Diet in Renal Disease and Cockcroft—Gault equations

Estimates of renal function are widely used in clinical practice and research. We assessed the performance of the Cockcroft—Gault (CG) and the Modification of Diet in Renal Disease (MDRD) equations in lupus nephritis patients. Data from ninety-seven lupus nephritis patients in the Hopkins Lupus Cohort were reviewed. Two renal function estimates, the CG and the MDRD, were compared with the 24 h creatinine clearance (CrCl). In the entire group of patients, the CG and MDRD equations had good global agreement with CrCl (R-square = 0.91 and 0.69, respectively). On average the CG equation overestimated CrCl by 2.36 mL/min/1.73 m2, whereas the MDRD equation underestimated CrCl by 5.85 mL/min/1.73 m2, P = 0.0004. The CG equation had greater accuracy (mean squared error) than the MDRD equation (14.93 versus 28.47 mL/min/1.73 m2, P = 0.002) when predicting CrCl. Although both equations lacked precision (standard deviation of the difference scores) in patients with CrCl ≥ 60 mL/min/1.73 m2, the CG equation was more precise than the MDRD equation in this group, (15.68 versus 29.58 mL/min/1.73 m2, P = 0.003). In lupus nephritis patients, the CG equation was superior to the MDRD equation as an estimate of CrCl. However, both equations lacked precision in patients with CrCl ≥ 60 mL/min/1.73 m2. Lupus (2007) 16, 887—895.