Correlation of methods of glomerular filtration rate estimation: Cockcroft-gault equation, modification of diet in renal disease, chronic kidney disease epidemiology collaboration, and DTPA renography in prospective renal donors -a retrospective analytical study

Introduction: The gold standard method for estimating glomerular filtration rate (GFR) in potential donors is diethylenetriaminepentaacetic acid (DTPA) renogram. But DTPA renogram being inconvenient, expensive, and with limited access , hence we need other methods which are noninvasive and provide a comparatively accurate estimation of GFR. Various estimating equations such as Cockcroft-Gault (CG) equation, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) are available but have not been well studied or compared to DTPA GFR measurement. Methods: A total of 100 healthy donors (females and males) were studied. All participants underwent 99mTc DTPA renogram, and the GFR obtained was compared with MDRD, CG, and CKD-EPI-estimated GFR. Correlation between variables was estimated by statistical analyses in SPSS software version 18.0, and accuracy of various methods was studied. The data were analyzed by paired t-test, and Pearson's correlation test was used to correlate between two variables. Results: Out of the 100 donors, 79% were females and out of 100 renal recipients, 88% were males. The mean age for donors was 47.27 +/- 10.93 years and for recipients was 35.02 +/- 11.11 years. The mean GFR (mL/min per 1.73 m2) obtained by DTPA, CG, MDRD, and CKD-EPI was 109.91 +/- 20.3, 114.10 +/- 21.25, 128.66 +/- 22.69, and 108.86 +/- 12.72, respectively. The overall mean bias was smallest for CKD-EPI (standard deviation: 18.79). The bias and mean absolute difference between calculated and measured GFR for CKD-EPI, MDRD, and CG were 8.98 and 16.05, -17.97 and 23.26, and -5.76 and 23.29, respectively. There was a positive correlation between GFR by DTPA and GFR by CKD-EPI (0.408) and MDRD (0.399). Conclusions: Despite a wide variation in absolute values of GFR obtained by these methods, CKD-EPI and MDRD showed a positive correlation with DTPA GFR. CKD-EPI had least bias and thus correlated best with DTPA. In potential donors, these equations may be inadequate to replace DTPA for estimating GFR and due to limitations of our study further studies are needed with bigger sample size and longer duration.