• Sarah Davis, David Huber, Karumathil M Murali, and Kelly Lambert.
• Department of Nephrology, Illawarra Shoalhaven Local Health District, Wollongong, New South Wales, Australia.
• Intern Med J. 2022 Oct 1; 52 (10): 177317791773-1779.

BackgroundRenal resistive index (RRI), which reflects intrarenal arterial impedance, is routinely measured when undertaking renal Doppler ultrasonography (RDU). Increased RRI has been suggested to reflect renal parenchymal disease and imply risk of kidney disease progression. But this has been disputed and extra-renal haemodynamic factors rather than intra-renal factors have been proposed to determine RRI.AimsTo investigate the relationship between elevated RRI and presence of chronic kidney disease (CKD), and examine whether elevated RRI at baseline is associated with decline in estimated glomerular filtration rate (eGFR) on follow up.MethodsThis retrospective observational study examined the association of elevated RRI (>0.7) with the presence of CKD (eGFR < 60 mL/min for >3 months), demographic and clinical factors in multivariable models. We also examined the effect of elevated RRI on eGFR decline on follow up using mixed models.ResultsOf the 346 patients undergoing RDU (median age 69.7 years; 46.2% male), 180 had elevated RRI. There was a strong inverse association between RRI and eGFR at baseline, 1 and 2 years (rho = -0.53, -0.51, -0.53, all P < 001). Elevated RRI was independently predicted by older age (odds ratio 3.29; 95% confidence interval 2.25-4.8; P < 0.001) and diabetes (odds ratio 2.65; 95% confidence interval 1.21-5.80; P = 0.015), but not CKD using multivariate logistic regression. Decline of eGFR was not different between RRI categories on follow up.ConclusionElevated RRI was predicted by older age and diabetes, but not by the presence of CKD. Baseline RRI was not associated with eGFR decline.© 2021 Royal Australasian College of Physicians.

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