A venous reflux study is a noninvasive ultrasound test that checks whether the valves inside your leg veins are working properly. It produces a map of healthy and unhealthy veins that a vascular specialist uses to determine if faulty valves are causing your symptoms and whether you’d benefit from treatment. The test is also called a venous insufficiency study or venous incompetence study.
Why the Test Is Ordered
Veins in your legs contain one-way valves that keep blood moving upward toward your heart. When those valves weaken or fail, blood flows backward and pools in the lower legs. This is called venous reflux, and over time it can cause a range of problems from cosmetic varicose veins to serious skin damage and open wounds.
Your doctor may order a venous reflux study if you have symptoms like aching, heaviness, tightness, swelling, skin irritation, itching, tingling, or muscle cramps in your legs, especially if those symptoms get worse as the day goes on or after prolonged standing. The test is also used when varicose veins haven’t improved with initial treatments like compression stockings, or when a specialist needs to plan a procedure to eliminate problem veins.
Vein problems are graded on a clinical scale from C0 (no visible signs) through C6 (an active skin ulcer). Mild cases involve spider veins or small varicose veins. More advanced stages include persistent swelling, skin discoloration, hardened or leathery skin around the ankles, and ulcers that have healed or remain open. The reflux study helps pinpoint which veins are responsible, regardless of where you fall on that spectrum.
What Happens During the Test
The study uses duplex ultrasound, which combines a standard ultrasound image of your vein structure with Doppler technology that measures the speed and direction of blood flow. A technician (sonographer) applies gel to your leg and moves a handheld probe along the skin, following the course of each vein from the groin or behind the knee down to the ankle.
You’ll typically stand during the exam. The leg being tested is rotated slightly outward, and you shift most of your weight onto the opposite leg. Standing is important because gravity pulls blood downward, which is exactly the condition that exposes a faulty valve. If you can’t stand for an extended period, the sonographer can position you lying down with your feet angled 15 to 20 degrees lower than your heart to simulate the effect of gravity.
At various points, the sonographer will squeeze your calf or foot and then release it. This “augmentation maneuver” pushes blood upward through the vein, producing a sharp spike of flow on the Doppler readout. When the squeeze is released, the valves should snap shut and stop blood from falling back down. If instead the Doppler shows blood reversing direction for longer than a set threshold, that segment of vein has reflux.
You may also be asked to bear down as if straining (a Valsalva maneuver), which increases pressure in the abdomen and challenges the valves near the top of the leg. The sonographer examines veins in both cross-section and lengthwise views, using probes tuned to frequencies between 9 and 13 MHz for detailed imaging.
How Long It Takes
A standard venous duplex ultrasound of the legs takes about 15 to 30 minutes. A full venous insufficiency study, which maps reflux patterns across the entire leg, typically takes longer: one to two hours, depending on whether one or both legs are examined. The test is painless. The calf squeezes feel like a firm grip, and the ultrasound probe causes no discomfort.
How Reflux Is Measured
The key measurement is how long blood flows backward after the valve is challenged. International guidelines set the cutoff at 0.5 seconds for most veins, including the great saphenous vein (the long vein running from the inner ankle to the groin) and the small saphenous vein (behind the calf). If reverse flow lasts 0.5 seconds or longer, that vein is considered to have significant reflux. For the deeper veins in the thigh and behind the knee, the threshold is slightly longer at 1 second.
The great saphenous vein is the most commonly affected, accounting for roughly 83% of superficial vein insufficiency cases. The small saphenous vein is involved about 11% of the time. The sonographer also checks where along the vein the reflux starts and stops, because the pattern matters for treatment planning. Some people have reflux only in a mid-thigh segment, while others have it running the full length of the vein from groin to ankle.
Preparation and Limitations
There’s no special preparation needed. You don’t need to fast or stop medications. Wear loose-fitting pants or shorts so the sonographer can access your legs easily. The main limitation is physical: if you have a cast, heavy bandaging, or a condition that prevents you from standing or holding still for an extended period, the test may be difficult to perform or may need to be modified.
What the Results Tell Your Doctor
The study produces a detailed map showing which veins are functioning normally and which have leaking valves, along with the severity and location of each reflux segment. This information serves two purposes. First, it confirms whether venous reflux is actually the cause of your symptoms, since leg pain, swelling, and skin changes can have other explanations. Second, it guides treatment decisions by identifying exactly which veins need to be addressed.
If reflux is found, treatment options range from conservative approaches like graduated compression stockings to procedures that close off the damaged vein. Endovenous ablation, which uses heat or a chemical to seal the vein from the inside, is one of the most common interventions. The body reroutes blood through healthier veins afterward. Follow-up ultrasounds are typically performed after any procedure to check for complications and confirm the treated vein has stayed closed.
In some cases, the study reveals that deeper veins are involved, not just the surface veins you can see bulging under the skin. About one in five people with varicose veins show some degree of deep vein valve failure, which can change the treatment approach. Certain small connecting veins near the ankle, called perforator veins, may also show reflux. These are particularly relevant in patients with skin ulcers, because they can keep feeding backward flow even after other veins are treated.