Accuracy of the methods used to estimate glomerular filtration rate compared to 24-hour urinary creatinine clearance in patients with chronic spinal cord injury

Abstract

Objective: To compare the accuracy of glomerular filtration rate (GFR) estimation by 24-hour urinary creatinine clearance with GFR estimation by the Modification of Diet in Renal Disease (MDRD) equation, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, the Mayo Clinic Quadratic equation (MCQE), and the modified Cockcroft–Gault formula in patients with spinal cord injury (SCI). Design: Cross-sectional study. Participants: Fifty-nine consecutive subjects, who were admitted to our hospital SCI rehabilitation and no additional acute medical disorders, were enrolled in this study. A 24-hour urine sample was collected for the determination of 24-hour urinary creatinine clearance, which was assumed as the standard technique for estimation of the GFR. The accuracy of several estimation formulas includes the 4-variable MDRD equation, the 6-variable MDRD equation, the Cockcroft and Gault equation, the CKD-EPI equation, and the MCQE. Results: GFRs calculated by the Cockcroft–Gault equation and 4-variable MDRD were significantly different from the 24-hour urinary creatinine clearance, whereas there were no significant differences in GFRs calculated by CKD-EPI (P = 1.000), Mayo Clinic Quadratic formula (P = 0.794), and 6-variable MDRD equations (P = 0.435) and 24-hour urinary creatinine clearance. Both the 6-variable MDRD equation and CKD-EPI were accurate within ±20 of the reference methods in 52.54% of the subjects. Conclusions: Among the methods used for estimation of the GFR including the 4- and 6-variable MDRD, the CKD-EPI, the modified Cockcroft–Gault equation, and the MCQE, the 6-variable MDRD equation and the CKD-EPI demonstrated best performance to estimate the GFR. However, none of the formulas were sufficient to estimate the GFR in SCI patients accurately.