Objective To investigate the effect of different kidney depth estimation formulas modified using SPECT/CT renal dynamic imaging on the calculation of the glomerular filtration rate (GFR) in living kidney transplant donors.

Methods The clinical data of 127 healthy kidney transplant donors who underwent preoperative ⁹⁹Tc^m-diethylene triamine pentoacetic acid (DTPA) renal dynamic imaging in the First Affiliated Hospital of Xi'an Jiaotong University from October 2011 to December 2017 were retrospectively analyzed. Included 36 males and 91 females, aged (49.2±7.3) years. The computed GFR of kidney depth measured via CT was adopted as the standard reference standard. The Tønnesen and Itoh formulas were used to calculate kidney depth and the corresponding GFR and then compare them with the CT results. The measurement data that did not conform to the normal distribution were expressed as M (Q₁, Q₂), and the Wilcoxon rank sum test was used to compare between the renal depth calculated by each formula. Spearman correlation analysis and linear regression analysis were used to analyze the correlation between renal depth and the corresponding GFR of lelf and right kidney by each formula.

Results The depth of the left and right kidneys from 127 healthy kidney transplant donors measured via CT 7.03(6.34, 7.67) cm, 7.21(6.51, 8.13) cm was significantly higher than those obtained using the Tønnesen formula 5.66(5.30, 6.06) cm, 5.70(5.33, 6.10) cm and the Itoh formula 6.70(6.33, 7.10) cm, 6.88(6.52, 7.26) cm, and the differences were statistically significant (left kidney: Z=−9.53, −3.77, both P<0.001; right kidney: Z=−9.73, −4.64, both P<0.001). The renal depth measured via CT was positively correlated with the renal depth calculated using the Tønnesen and Itoh formulas (left kidney: r=0.330, 0.331, both P<0.001; right kidney: r=0.359, 0.358, both P<0.001). The GFR of left and right kidneys that corresponded to the renal depth measured via CT 46.4(39.9, 52.0) ml/min, 46.0(40.5, 54.9) ml/min was higher than those obtained using the Tønnesen formula 36.6(33.0, 41.9) ml/min, 36.2(32.1, 40.1) ml/min and the Itoh formula 43.2 (39.4, 49.8) ml/min, 43.8 (39.4, 48.7) ml/min, and the differences were statistically significant (left kidney: Z=−9.52, −3.76, both P<0.001; right kidney: Z=−9.73, −4.75, both P<0.001). The CT measurement was positively correlated with the GFR values that corresponded to kidney depth estimates obtained using the Tønnesen and Itoh formulas (left kidney: r=0.476, 0.476, both P<0.001; right kidney: r=0.386, 0.539, both P<0.001).

Conclusions The GFR calculated using the Tønnesen and Itoh formulas are suitable for the routine screening and evaluation of kidney diseases. For kidney transplant donors with more stringent requirements for renal GFR, kidney depth measured via CT should be used to correct the GFR calculated using SPECT/CT.