Assessment of Split Renal Function Using a Combination of Contrast-Enhanced CT and Serum Creatinine Values for...

OBJECTIVE. The objective of our study was to develop a novel method to estimate single-kidney glomerular filtration rate (GFR) using a combination of contrast-enhanced CT and serum creatinine (SCr) values and to validate the resulting estimated glomerular filtration rates (eGFRs) by comparing them with the single-kidney Gates GFR, which is based on renal dynamic imaging. MATERIALS AND METHODS. Sixty-two patients with asymmetric renal disease who underwent unenhanced and triphasic contrast-enhanced CT of the kidneys, ^99mTc-diethylenetriamine pentaacetic acid renal dynamic imaging, and SCr testing within 1 week were retrospectively included. The eGFR was split into single-kidney GFRs of the left and right kidneys by a proportionality factor derived from the products of renal volume and CT number increments of the multiphasic CT images, which produced unenhanced phase (yielded by the renal volume proportional factor alone), arterial phase, venous phase, and nephrographic phase CT split eGFRs. The four CT split eGFRs were compared with the Gates GFR using the paired-sample t test, Pearson correlation analysis, and Bland-Altman analysis. RESULTS. Correlation coefficients and 95% CIs between the four CT split eGFRs and Gates GFR were as follows: unenhanced phase, 0.729 (95% CI, 0.626-0.805); arterial phase, 0.781 (95% CI, 0.685-0.849); venous phase, 0.788 (95% CI, 0.690-0.839); and nephrographic phase, 0.842 (95% CI, 0.758-0.902) (all, p < 0.001). The paired differences between the CT split eGFRs and Gates GFR were as follows: unenhanced phase, 2.04 ± 10.85 (95% CI, 0.01-4.07) mL/min/1.73 m²; arterial phase, 2.04 ± 10.56 (95% CI, 0.06-4.02) mL/min/1.73 m²; venous phase, 2.04 ± 10.04 (95% CI, 0.16-3.92) mL/min/1.73 m²; and nephrographic phase, 2.04 ± 8.92 (95% CI, 0.37-3.71) mL/min/1.73 m². These results suggest a maximum deviation from the Gates GFR of ± 44.9% for the unenhanced phase eGFR, ± 43.7% for the arterial phase eGFR, ± 41.6% for the venous phase eGFR, and ± 36.9% for nephrographic phase eGFR. CONCLUSION. Split renal function can be estimated using a combination of contrast-enhanced CT and SCr values to calculate eGFR. The CT images of the nephrographic phase may be the optimal choice to use in this proposed method.