*Purpose: The ¹²⁵I-iothalamate clearance and ^99mTc-DTPA split scan nuclear medicine studies are used among living kidney donor candidates to determine mGFR and split-scan ratio (SSR). The CT-derived cortical-volume ratio (CVR) is a novel measurement of split-kidney function and can be combined with pre-donation eGFR or mGFR to predict post-donation kidney function. Whether pre-donation SSR predict post-donation kidney function better than pre-donation CVR and whether pre-donation mGFR provides additional information beyond pre-donation eGFR is unknown.

*Methods: We performed a single-center retrospective study of 204 patients who underwent kidney donation between 06/2015-03/2019. The primary outcome was 1-year post-donation eGFR. Model bases were created from a measure of pre-donation kidney function (mGFR or eGFR) multiplied by the proportion that each non-donated kidney contributed to pre-donation kidney function (SSR or CVR). Multivariable elastic net regression with 1,000 repetitions was used to determine the mean and 95%CI of R2, root mean square error (RMSE), and proportion overprediction ≥15 mL/min/1.73m² between models.

*Results: In validation cohorts, eGFR-CVR models performed best (R² 0.547, RMSE 9.2 mL/min/1.73m², proportion overprediction 3.1%) whereas mGFR-SSR models performed worst (R² 0.360, RMSE 10.9 mL/min/1.73m², proportion overprediction 7.2%) (P<.001 for all comparisons). R² and RMSE distributions are shown in Figures. The eGFR-CVR models had the smallest residuals among the lowest baseline eGFR decile (Figure).

*Conclusions: These findings suggest that pre-donation CVR may serve as an acceptable alternative to SSR during donor evaluation and furthermore that a model based on CVR and pre-donation eGFR may be superior to other methods.

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