Renal arterial resistive index

Last revised by David Carroll on 24 Feb 2021

The renal arterial resistive index (RI) is a sonographic index of intrarenal arteries defined as (peak systolic velocity - end-diastolic velocity) / peak systolic velocity. The normal range is 0.50-0.70. Elevated values are associated with poorer prognosis in various renal disorders and renal transplant.

The resistive index (RI) is measured using spectral Doppler at the arcuate arteries (at the corticomedullary junction) or interlobar arteries (adjacent to medullary pyramids).

The resistive index is thought to reflect central hemodynamic (cardiac or aortic) characteristics rather than properties of the kidney itself 10,11. Some have proposed that since it reflects pulsatility and vascular compliance, it would be more appropriately called an impedance index 13.

The renal resistive index is a nonspecific prognostic marker in vascular diseases that affect the kidney. High resistive indices (>0.8) in native kidneys are associated with renal dysfunction and adverse cardiovascular events 7,8. In renal transplant recipients, high resistive indices (>0.8) are associated with increased risk of graft loss and death 9. There is thought to be little correlation between the resistive indices and the quantitative extent of renal dysfunction (measured by serum creatinine values) 2.

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