*Purpose: Perfusion parameters are increasingly used to assess the quality of organs and to make decisions about discarding the organ. Resistive index(RI) has been an important parameter that has shown correlation with both immediate and late graft outcomes. An RI value of >0.25 has been studied in the literature as a suboptimal perfusion parameter which has predictive value for outcome. Our aim was to evaluate whether final RI >0.25 is predictive of delayed graft function(DGF), primary non-function(PNF) and 3-mo estimated glomerular filtration rate(eGFR).

*Methods: We retrospectively analyzed baseline characteristics and outcomes for machine perfused kidney transplants at our center between 08/2020 and 06/2021. All kidneys were pumped on a Lifeport kidney transporter at our local procurement center. Independent predictors of DGF and 3-mo eGFR(ml/min/1.73m²) were identified using multivariable stepwise logistic regression analysis. We then categorized final RI values into groups (<0.25,0.25-0.34, and >0.35) to show its ability to predict DGF, PNF, and 3-mo mean eGFR(+SE).

*Results: A total of 287 recipients were analyzed; mean RI was 0.25+0.01 [median=0.24, range:0.09-0.56]. Overall, the percentage developing DGF and PNF was 31.0%(89/287) and 2.8%(8/287), respectively. Mean 3-mo eGFR was 59.1+1.6. A higher RI (as a continuous variable) was independently associated with higher %DGF(p=0.02) and lower 3-mo eGFR(p=0.009); a trend also existed for an association of higher RI with greater death-censored graft failure. When considering RI categories of <0.25,0.25-0.34, and >0.35, differences in development of DGF and PNF were not significant (28.8% vs 29.4% vs 43.6% for DGF, p=0.19; and 2.1% vs 2.0% vs 7.7% for PNF, p=0.13). The 3-mo mean eGFR was lower for RI >0.35 and RI 0.25-0.34 compared to RI <0.25 (53.5 +3.2 and 54.0 +2.8 vs. 64.2+2.3; p=0.006).

*Conclusions: A higher final RI was independently associated with greater DGF, PNF, and a lower 3-mo eGFR; hence, it provides a valuable tool in assessing early quality of the donor organ. An RI >0.25 appears to be associated with inferior 3-mo mean eGFR. Whether final RI can be used with other significant donor, pump, and recipient variables to make a reliable predictive model that can help to judiciously select donor-recipient combination and to predict early and late graft outcomes will depend on further studies.

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