In duplex Doppler assessment for renal artery stenosis, a peak systolic velocity in the renal artery greater than 180 cm/s is often associated with which resistive index ratio value?

• A. 2.0
• B. 3.5
• C. 4.0
• D. 5.0

Answer: (B)

When renal artery narrowing reaches a level that pushes the peak systolic velocity above 180 cm/s, the diastolic portion of the waveform often diminishes, causing the systolic-to-diastolic ratio to rise. The ratio of peak systolic velocity to end-diastolic velocity (often called the S/D ratio) tends to be around 3.5 in this scenario, reflecting a hemodynamically significant stenosis with higher downstream resistance. So, a value near 3.5 best matches the pattern you’d expect when PSV exceeds 180 cm/s.

Normal or mildly abnormal flow would have a lower S/D ratio (around 2.0), while markedly higher ratios like 4.0 or 5.0 would suggest even more pronounced impedance not typically tied to the stated PSV threshold.