Introduction: Atherosclerosis of the aorto-iliac vessels can adversely affect kidney perfusion after kidney transplantation (KTx). Post-transplantation kidney perfusion can be determined by the intrarenal resistance index (RI) using Doppler ultrasound (DUS). The severity of atherosclerosis can be determined by means of the Calcium Score (CaScore). This study investigates the association between aorto-iliac CaScore and RI in kidney transplant recipients.

Methods: Kidney transplant recipients (2004-2019), for which a CaScore and an RI could be determined, were included in this dual-center cohort study (n=389). The CaScore was measured, by means of the Agatston score, in three aorto-iliac segments using non-contrast CT imaging. The RI ((peak systolic rate - end diastolic rate) / peak systolic rate) was determined by DUS. Multivariable linear regression analysis was performed between the CaScore and the RI adjusted for confounding variables which are found with multiple univariate regression analyses.

Results: Median (IQR) RI score (unitless) was 0.70 (0.64 to 0.77) and CaScore (unitless) was 3340 (399 to 7833). In univariate linear regression analyses, with RI as dependent variable, CaScore (β=0.008; 0.004 to 0.013; P<0.001) was associated with RI. In addition, age of the recipient (β=0.091; 95%CI 0.039 to 0.143; P=0.001), history of diabetes (β=0.018; 0.005 to 0.030; P=0.005), history of vascular intervention (β=0.020; 0.007 to 0.033; P=0.002), prior dialysis (β=0.018; 0.006 to 0.029; P=0.003), deceased donation (β=0.026; 0.015 to 0.037; P<0.001), cold ischemia time (β=0.036; 0.020 to 0.052; P<0.001) and preoperative diastolic blood pressure (β=-0.098; -0.174 to -0.021 P=0.013) were associated with RI. In multivariable analysis, CaScore and RI remained significantly (P=0.023) associated, independent of adjustment for potential confounders.

Conclusion: A significant association was found between the CaScore and RI after adjustment for multiple recipient and donor confounding factors. Aorto-iliac atherosclerosis should be taken into account when interpreting the RI and determining the cause of malperfusion and graft failure after kidney transplantation.