Comparison of glomerular filtration rate measured between anterior and posterior image processing using Gates’ method in an ectopic pelvic kidney

OBJECTIVE The aim of this study was to evaluate the difference in measured glomerular filtration rate (GFR) of an ectopic pelvic kidney between anterior and posterior image processing using Gates' method of renal dynamic imaging. METHODS A total of 10 patients were studied retrospectively, with a single ectopic kidney in the pelvic cavity and a contralateral kidney at its normal anatomical position confirmed by ultrasound, computed tomography, renal dynamic imaging, etc. All images of ectopic kidneys were processed, and GFRs were measured using anterior and posterior Gates' method of renal dynamic imaging, respectively. The contralateral normal kidney was only processed on posterior imaging. The total GFRant of one patient, which was equal to the sum of the GFR of a normal kidney on posterior imaging and the GFR of an ectopic kidney on anterior imaging, was compared with the total GFRpost of two kidneys on posterior imaging, with the GFRtwo-sample from the two-sample method, and with the estimated GFR in the Chronic Kidney Disease Epidemiology Collaboration equation. All correlation analyses were carried out between GFRs obtained from three methods, and all patients were followed up. For statistical analysis, nonparametric rank tests were used, Bland-Altman graphs were plotted. RESULTS The mean GFR of the ectopic kidney on anterior imaging was 27.48±12.24 ml/min/1.73 m. It was higher than the GFR (10.71±4.74 ml/min/1.73 m) on posterior imaging (t=-2.803, P<0.05). There were statistical differences between the total GFRant and the total GFRtwo-sample (Z=-2.295, P<0.05), between the total GFRant and the total GFRpost (Z=2.599, P<0.01), between the total GFRtwo-sample and the total GFRpost (Z=-2.191, P<0.05), and between the total GFRant and the estimated glomerular filtration rate (Z=-2.803, P<0.01). The bias of the total GFRant was different from that of the total GFRpost (Z=-2.191, P<0.05). There were no differences in the precision and accuracy within 30% of the total GFRant and that of the total GFRpost (precision: F=0.351, P>0.05), but there were statistical differences in the accuracy within 10% of the total GFRant and that of the total GFRpost (P<0.05). CONCLUSION The GFR measured using Gates' method of anterior image processing was more accurate than the GFR obtained on posterior image processing in reflecting the function of an ectopic pelvic kidney in renal dynamic imaging.