Comparison of three glomerular filtration rate estimating equations with 24-hour urine creatinine clearance measurement in live kidney donors
Fernando Giron Luque1, Andrea Garcia Lopez1, Nasly Patiño Jaramillo1.
1Bogota D.C, Colombiana de Trasplantes, Bogota, Colombia
Background: It is very important to determine as accurately as possible the renal function in potential living kidney donors (PLKD). The direct measurement of glomerular filtration rate (mGFR) has been considered the “gold standard” for the kidney failure evaluation. Nonetheless, these are not available in many medical centers due to the complexity of the technique. The estimated GFR with 24-hour urinary creatinine clearance (ClCr) is frequently used because of its availability. In this study we aim to compare the different eGFR using serum-based creatinine formulas (Cockcroft-Gault, MDRD and CKD-EPI) and the eGFR based on 24-hour urinary creatinine clearance to determine the usefulness of eGFR creatinine formulas to evaluate kidney function in PLKD.
Methods: We evaluate kidney function in 799 PLKD using 24-hour urinary ClCr method. The GFR obtained was compared with eGFR based on creatinine (Cockcroft-Gault, MDRD and CKD-EPI). We calculated mean bias (difference), precision (SD of this difference), accuracy (proportion of eGFR within ±10% of ClCr GFR) and performed Bland-Altman-plots.
Results: Using the Bland Altman graphic, we observed that the most dispersed results are obtained using MDRD. Smallest mean bias and was observed for Cockcroft-Gault (bias of 5.8; SD 25.1) compared to the other equations (CKD-EPI: bias of 9.8; SD 24.8 and MDRD: bias of 13.8; SD 25.3). Smallest bias was found in females for the three equations. Results of mean bias were similar when comparing the three equations in patients with ClCr GFR < 60, however, smaller mean bias were found for the three equations above age 40 years. Regarding the assessment of the 95% limits of agreement (LoA), we found a high dispersion for the three equations being the highest upper limit of agreement 63.5 (MDRD) and the highest lower limit of agreement -43.4 (Cock-roft-Gault).
Conclusion: In this PLKD cohort, Cockcroft-Gault equation showed the highest approximation to the reference method. The interval range was too big to assume equivalence between 24-hour urinary ClCr method and eGFR based on creatinine (Cockcroft-Gault, MDRD and CKD-EPI).
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