Abstract
Duplex-Doppler ultrasonography has become an essential tool in the diagnosis and management of kidney diseases, allowing clinicians to assess renal hemodynamics, detect vascular abnormalities, and monitor disease progression. Among the various Doppler-derived parameters, the renal resistive index (RRI) has gained particular attention both as a diagnostic tool and a prognostic marker in nephrology. Traditionally considered an indicator of parenchymal perfusion, recent evidence highlights its strong association with systemic hemodynamic factors, particularly arterial stiffness, positioning RRI as a valuable tool for evaluating patients with systemic vascular impairment, such as hypertension, diabetes mellitus, and atherosclerosis. RRI has been strongly linked to vascular damage, which in turn is influenced by inflammation and endothelial dysfunction, making it a reliable marker of cardiovascular damage and a potential predictor of cardiovascular risk. Furthermore, emerging studies suggest that RRI could serve as a dynamic parameter to monitor vascular changes induced by therapeutic interventions. This narrative review summarizes the classic and evolving applications of RRI, from its origin as a renal hemodynamic marker to its emerging role as a systemic vascular biomarker with diagnostic and prognostic significance in cardiovascular and metabolic diseases.