Which criterion defines abnormal venous reflux on duplex ultrasound?

• A. Retrograde flow persists for more than 0.5 seconds in a superficial or deep venous segment.
• B. Inability to demonstrate any retrograde flow during provocative maneuvers.
• C. Continuous anterograde flow during provocative maneuvers.
• D. Reflux confined to perforator veins only.

Answer: (A)

The key idea is how we define abnormal venous reflux on duplex ultrasound by the duration of backward flow after a provocative maneuver. If the retrograde flow lasts longer than 0.5 seconds in a superficial or deep venous segment, that indicates valvular incompetence and abnormal reflux. This 0.5-second cutoff helps separate normal, transient reflux—which can occur with coughing, Valsalva, or other maneuvers—from true pathologic reflux due to incompetent valves. The criterion applies to both superficial and deep veins, not just perforators, and persistent reflux beyond 0.5 seconds is the hallmark of abnormal venous reflux. Short-lived retrograde flow or no retrograde flow suggests normal valve function, and reflux confined only to perforator veins indicates localized issues but does not define abnormal reflux in the main superficial/deep venous system by this standard.