Elevated renal resistive index (RRI) and significant proteinuria were independent predictors of chronic kidney disease (CKD) progression over 2 years, according to findings published in the Journal of Clinical Medicine.

“When the interaction was investigated, an elevated RRI was associated with higher CKD progression in both [patients who were non-proteinuric and proteinuric], whereas proteinuria had a significantly negative impact only in patients with no elevated RRI,” GianLuca Colussi, MD, and colleagues wrote.

The study included 156 patients with CKD of unknown origin from a nephrology outpatient clinic. The researchers investigated the effect of a high RRI, a measure of intrarenal blood flow by echo-color Doppler ultrasound (≥0.80 was considered elevated), and significant proteinuria (urinary protein excretion ≥150 mg/day) on kidney function decline or new-onset endstage kidney disease (ESKD) after 2 years of follow-up. The effect of high RRI together with significant proteinuria on the combined endpoint was also considered.

“Dominant Role” of RRI as Marker of CKD Progression

At the 2-year follow-up, 32% of patients met the study endpoint of kidney function decline or new-onset ESKD.

A multivariate logistic model identified an elevated RRI and significant proteinuria as independent predictors. Odds ratios for meeting the combined endpoint were 4.28 with an elevated RRI and 3.59 with significant proteinuria, according to the study.

The prevalence of kidney function decline or new-onset ESKD was 65.2% in patients with both an elevated RRI and significant proteinuria, 42.3% in patients with only an elevated RRI, 39.5% in patients with only proteinuria, and 10.9% in patients with neither.

The study also found increased RRI and 24- hour urinary protein excretion were inversely and independently associated with percent change in eGFR. Patients with elevated RRI and significant proteinuria had a higher percentage reduction at 2 years (-38.0% ±20.4%) than patients with only proteinuria (-25.3% ±19.0%) or patients without elevated RRI or proteinuria (-8.8% ±25.1%). Patients with elevated RRI alone had a percentage change of -29.6% ±21.0%.

“Although these findings must be confirmed in prospective studies, the apparent dominant role of the RRI as a marker of CKD progression independent of proteinuria suggests that it should be evaluated in all patients with CKD of unknown origin,” Dr. Colussi and colleagues wrote.