Background: Our hypothesis was that both the Chronic KidneyDisease-Epidemiology Collaboration (CKD-EPI) and Modification of Diet in RenalDisease (MDRD) equations would underestimate directly measured GFR (mGFR) to asimilar extent in people with diabetes and preserved renal function.
Methods: In a cross-sectional study, bias (eGFR – mGFR) wascompared for the CKD-EPI and MDRD equations, after stratification for mGFRlevels. We also examined the ability of the CKD-EPI compared with the MDRDequation to correctly classify subjects to various CKD stages. In alongitudinal study of subjects with an early decline in GFR i.e., initial mGFR>60 ml/min/1.73 m2 and rate of decline in GFR(ΔmGFR) > 3.3 ml/min/1.73 m2per year, ΔmGFR (based on initial andfinal values) was compared with ΔeGFR by the CKD-EPI and MDRD equations over amean of 9 years.Results: In the cross-sectional study, mGFR for the wholegroup was 80 ± 2.2 ml/min/1.73 m2 (n = 199, 75 % type 2 diabetes). For subjects with mGFR>90 ml/min/1.73 m2 (mGFR: 112 ± 2.0, n = 76), both equations significantly underestimated mGFR to asimilar extent: bias for CKD-EPI: -12 ± 1.4 ml/min/1.73 m2 (p < 0.001) and for MDRD:-11 ± 2.1 ml/min/1.73 m2 (p < 0.001). Using the CKD-EPI compared with the MDRDequation did not improve the number of subjects that were correctly classifiedto a CKD-stage. No biochemical or clinical patient characteristics wereidentified to account for the under estimation of mGFR values in the normal tohigh range by the CKD-EPI equation. In the longitudinal study (n = 30, 66 % type 1 diabetes), initial and final mGFRvalues were 102.8 ± 6 and 54.6 ± 6.0 ml/min/1.73 m2, respectively.Mean ΔGFR (ml/min/1.73 m2 per year) was 6.0 by mGFR compared withonly 3.0 by MDRD and 3.2 by CKD-EPI (both p < 0.05 vs mGFR)
Conclusions: Both the CKD-EPI and MDRD equations underestimatereference GFR values >90 ml/min/1.73 m2 as well as an earlydecline in GFR to a similar extent in people with diabetes. There is scope toimprove methods for estimating an early decline in GFR.