Renal Resistive Index (RRI) Calculator

Renal Resistive Index (RRI) by Doppler Ultrasound: Explanation and Clinical Context The Renal Resistive Index (RRI) is a non-invasive Doppler ultrasound parameter used to evaluate renal arterial resistance and kidney perfusion. It is calculated using the formula: RRI = (PSV - EDV) / PSV, where PSV is the peak systolic velocity and EDV is the end diastolic velocity of intrarenal arteries. Normal RRI values range between 0.56 and 0.70.

Elevated RRI values (>0.70) can indicate increased renal vascular resistance and are associated with conditions such as acute kidney injury, chronic kidney disease progression, renal transplant dysfunction, or renal artery stenosis. RRI provides clinicians with important prognostic and diagnostic information. In kidney transplantation, for example, higher RRI values early post-transplant correlate with delayed graft function and poor long-term renal outcomes.

In critically ill patients, it can help detect early renal perfusion abnormalities and guide hemodynamic management.