The renal arterial resistive index (RI) is a sonographic index to assess for renal arterial disease.
RI = (peak systolic velocity - end diastolic velocity ) / peak systolic velocity
- The normal value is ≈ 0.60
- With 0.8-0.9 being elevated
- The RI measures the resistance of renal arterial flow to the kidney. In cases that cause elevated RI levels, there is reduced flow through the renal artery during diastole and sometimes even reversal of flow during diastole.
We classically see this in the transplant kidney when there is concern for rejection
What is the differential diagnosis of this finding in a native kidney?
ATN
Obstruction
Obstruction
Renal artery stenosis
Renal vein thrombosis
Renal vein thrombosis
Pyelonephritis
Severe hypotension
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