Duplex Doppler Measurement of Renal Resistive Index in Non-Dialysis Chronic Kidney Disease Outpatients: A Proposed Standardized Protocol

The renal resistive index (RRI) is a Doppler-derived parameter influenced by intrarenal hemodynamics, vascular compliance, pulsatile load, and systemic cardiovascular factors. In outpatient nephrology practice, RRI may provide adjunctive hemodynamic and prognostic information when interpreted together with kidney morphology, estimated glomerular filtration rate, proteinuria, blood pressure, heart rate, rhythm, and cardiovascular context. This protocol aims to standardize duplex Doppler acquisition, calculation, interpretation, and reporting of RRI in outpatient adults with native-kidney chronic kidney disease (CKD). The protocol defines patient eligibility and preparation, same-visit clinical data collection, grayscale kidney assessment, color Doppler localization of intrarenal arteries, pulsed-wave Doppler settings, bilateral upper-, middle-, and lower-pole sampling, waveform validity criteria, RRI calculation rules, image archiving, and structured reporting. Technical pitfalls and hemodynamic confounders are incorporated into the workflow to support reproducibility and serial comparability. The expected output is a standardized RRI report including kidney-specific and bilateral mean RRI values when minimum validity criteria are met, the number and location of valid sampling sites, grayscale morphologic findings, same-visit hemodynamic context, relevant technical limitations, and interpretive caveats. The protocol is designed to reduce acquisition variability and improve the consistency of RRI documentation in outpatient CKD practice. RRI should not be interpreted as a stand-alone diagnostic test or direct surrogate of renal vascular resistance. A standardized acquisition and reporting protocol may improve reproducibility and allow RRI to be used more appropriately as an adjunctive hemodynamic and prognostic marker in adults with non-dialysis-dependent CKD.