Renal Resistive Index Along the Renal Arterial Tree: Do Kidney and Cardiovascular Associations Depend on the Measurement Site? A Scoping Review

Objective: The renal resistive index (RRI), measured by Doppler ultrasonography, is commonly used to assess renal vascular-interstitial damage. However, the RRI may be associated with cardiovascular and general hemodynamic factors, as well as with structural and functional changes within the kidney. These associations may be influenced by the measurement location of the RRI. This scoping review aimed to evaluate differences in RRI associations with hemodynamic or structural and functional alterations in the kidney across measurements at different sites along the renal arterial tree. Methods: A search of the PubMed database was conducted to identify studies evaluating the association between the RRI measured at different levels of the renal arterial tree. Separate search strategies were used for the main renal artery, segmental/interlobar arteries, and intraparenchymal cortical vessels. Studies were selected based on predefined inclusion and exclusion criteria. Results: A total of 888 publications were identified. After applying the exclusion criteria, the final analysis included 6 papers on main arteries, 30 on segmental arteries, and 7 on parenchymal arteries. All analyzed publications showed associations between the RRI and cardiovascular or renal factors, or both. Conclusions: Available data suggest that the relationship between the renal resistive index and systemic or local changes may vary by measurement site. However, reliable studies directly comparing RRI associations across measurement sites are lacking. Therefore, current evidence does not establish whether RRI measurements obtained at different sites can be used interchangeably.