Accuracy to estimate rates of decline in glomerular filtration rate in renal transplant patients

Background. We examined the use of the Cockroft Gault (C-G) test, Modified Diet in Renal Disease 2 (MDRD2) test, and inverse serum creatinine (Delta 1/Scr) to estimate rates of decline in renal transplant function using isotope glomerular filtration rate (GFR) as a reference test. Methods. Percent changes in estimated GFR (Delta eGFR) were compared to simultaneous changes in isotope GFR (Delta iGFR) in 72 patients. Results. The number of iGFR was 508 with a mean of 7.15 +/- 1.15 scans per patient. There was a decline in iGFR of 16.14 +/- 21.37 ml/min over the study duration of 88.9 +/- 57.6 months. Delta eGFR and Delta 1/Scr correlated significantly with Delta iGFR. Accuracy to predict Delta iGFR from the eGFRs was limited to < 65% concordance within 30% range from changes in iGFR. Slope analyses showed a significantly lower percent annual loss in mean iGFR of 6.03% than that of the C-G of 8.62% and MDRD2 of 8.96% (P < 0.001). The within patient variability measured from the standard deviation (ml/min) of root mean square of 4.69 for iGFR was significantly higher than that for C-G and MDRD2 of 2.46 and 2.94, respectively. iGFR and eGFR at first observation correlated significantly (P < 0.001) with last observation. Conclusions. iGFR is significantly more variable within patient than the other predictors, and the two estimators predict the iGFR with a high sensitivity but low specificity. This is a clinically reasonable combination. Predicted percent of annual loss in iGFR appears to be smaller than that using the two estimators.