The role of renal resistive index as a prognostic tool in kidney transplantation: a systematic review

Background In kidney transplant recipients (KTRs), observational data have reported conflicting findings about the utility of renal resistive index (RRI) in determining outcomes. This study aimed to synthesize the current literature and determine the prognostic role of RRI in KTRs. Methods The authors conducted a systematic review to assess the role of RRI in predicting death, graft failure, graft function and proteinuria. Of the 934 titles/abstracts reviewed, 26 studies were included. There was significant heterogeneity in RRI measurements and thresholds as well as in analytical methods, and a meta-analysis could not be performed. Results All included studies were observational and included 7049 KTRs. Eight studies analyzed death, of which five reported a significant association with higher RRI. In the remaining three, small sample sizes and lower/multiple RRI thresholds may have limited detection of a statistically significant difference. Three studies investigated all-cause graft failure, and an association with RRI was reported but varied by time of RRI measurement. Three out of five studies that analyzed a composite of patient and graft outcomes reported an association with RRI. Evidence analyzing death-censored graft failure, graft failure (unclear whether death-censored or all-cause), measures of graft function and proteinuria was conflicting. Most studies had a moderate to high risk of bias. Conclusions RRI likely has a prognostic role in predicting patient outcomes, reflecting patient systemic vascular disease burden rather than graft hemodynamics. Since cardiovascular diseases are a major cause of death and graft loss, RRI may be explored as a noninvasive tool to risk-stratify KTRs.