Establishment of a formula for the estimation of kidney depth in adults and its effect on glomerular filtration rate assessment

BACKGROUND: Gates’ analysis method for kidney depth (KD) calculation is the only way to determine the glomerular filtration rate (GFR) of the kidney in clinical practice, which posits that the influence of KD on the GFR is more important than other factors. Computed tomography (CT) measurement of the donor KD can improve the accuracy of GFR measurement by Gates’ method but will also increase the radiation exposure of kidney transplantation donors. Thus, it is particularly important to establish an accurate empirical formula for KD measurement that is more consistent with the real KD. METHODS: In total, 326 potential renal transplantation donors were enrolled in this study. Among these, 167 donors were assigned to the training set to estimate the regression formula of KD measured by CT. The remaining 159 donors were included in the validation set to verify the regression formula. The KD measured by CT and its corresponding GFR was taken as the reference standard. The performances of formulas were then compared. RESULTS: There was no significant statistical difference between the CT-measured KD and the current fitting, Li Q, and Xue JJ formulas (P>0.05). However, significant differences were observed between the KDs calculated using the Taylor, Ma G, and Uchiyama formulas and the CT-measured reference standard KD (P<0.05). Furthermore, there was no notable difference in the GFR(L) and GFR(R) corresponding to the CT-measured KD with that of the fitting, Ma G, and Xue JJ formulas (P>0.05). There were also marked differences in the GFR(R) corresponding to the Li Q’s formula (P<0.05), and in the GFR between other estimation methods and the CT measurement (P<0.05). CONCLUSIONS: The fitting formula established in this study can play a more important role if an accurate measurement method of the body thickness at the level of the hilum on the body surface can be found.