Background: Glomerular filtration rate estimates (e-GFR) are often used to evaluate the changes in renal function, but have not been validated for this purpose in kidney transplant recipients (KTRs). The aim of this study was to evaluate the validity of e-GFR for monitoring serial changes in renal function in KTR using directly measured GFR by inulin clearance (I-GFR) as the reference standard.
Methods: Performances of inverse serum creatinine (1/creat) and Cockcroft and Gault, Modification of Diet in Renal Disease, and Chronic Kidney Disease Epidemiology Collaboration formulas were assessed to estimate the changes in I-GFR.
Results: A total of 1935 I-GFR clearance procedures were performed in 631 KTRs who underwent serial measurements between 2003 and 2009. The baseline median I-GFR were 51.0 mL/min/1.73 m(2) (confidence interval 95%: 23-84 mL/min/1.73 m(2)]. The performances of 1/creat and formulas for detecting the I-GFR variations between two consecutive measurements (n = 1304) were similar. To detect the variations of <20% (increase or decrease), sensitivities ranged between 50 and 56%, and specificities between 64 and 69%. To detect the variations >20% (increase or decrease), sensitivities ranged between 27% and 39%, and specificities between 88 and 97%. Bland-Altman plots confirmed the scattering of values for individual patients.
Conclusions: In a population of Caucasian KTRs, the mean changes in GFR are correctly estimated whatever the formula used in the range of 23-84 mL/min/1.73 m(2) and can thus be applied in population studies. However, in clinical practice, individual changes in GFR evaluated by formulas should be interpreted with caution in KTRs.
Keywords: creatinine-based formulas; inulin clearance; kidney transplant; renal function estimation.