Evaluation of the influence of kidney depth in GFR with radionuclide renal scintigraphy

Objectives The aim of this study is to evaluate the effect of kidney depth in calculating GFR with radionuclide renal scintigraphy.

Methods The aim of this study is to evaluate the effect of kidney depth in calculating GFR with radionuclide renal scintigraphy. Methods 482 patients with chronic kidney disease (CKD) were enrolled. GFR were estimated simultaneously using modified Gate’s method (gGFR); Gate’s method with the verify formulae of depth (v-gGFR); and dual plasma sampling method (rGFR). gGFR and v-gGFR were compared with rGFR. In v-gGFR, instead of Tonnesen’s formula, which was used to estimate the renal depth in Gate’a methoe, we adopted the renal depth formula obtained in our previous study: right kidney depth (cm) = 15.449 × (weight/height) + 0.09637 × age + 0.782; right kidney depth (cm) = 16.772 × (weight/height) + 0.01025 × age + 0.224( weight, kg; height, cm). All statistics were performed using SPSS 10.0. The estimated gGFR and v-gGFR were compared using Bland-Altman analysis. The spearman correlation and linear regression were used to describe the relationship between gGFR/v-gGFR and rGFR. The precision was expressed as the width between the 95% limits of agreement.

Results Both gGFR and v-gGFR were correlated well with rGFR(r=0.75, P<0.0001; r=0.81, P<0.0001. In linear regressions against rGFR, v-gGFR displayed a smaller intercept; its slope was higher and much closer to the identical line than of gGFR. The difference and absolute difference between v-gGFR and rGFR were significantly less than those between gGFR and rGFR (median of -1.34 ml/1.73m2.min vs -2.71 ml/1.73m2.min, P<0.0001; median of 12.38 ml/1.73m2.min vs 15.63 ml/1.73m2.min, P<0.0001). For gGFR, the 15%, 30% and 50% accuracies were 32.43%,56.04% and 79.13%, respectively; for v-gGFR, the corresponding accuracy rose to 45.04%, 74.48% and 89.85%, respectively.

Conclusions In this research, the GFR obtained by the new formula of kidney depth was more accurate than GFR estimated by tradional radionuclide renal scintigraphy