Someone ran a probe along your leg and squeezed your calf. A few minutes later you were holding a page of abbreviations like GSV and SFJ, a column of numbers in milliseconds, and one line that says venous reflux with no explanation attached. You might fold the page, take it home, and search for it that night.
TL;DR
- Venous reflux: blood slipping backward through a leaky leg-vein valve
- Cutoffs: over 0.5 seconds in most leg veins, over 1 second in the large deep veins of the thigh and knee
- Standing vs. lying down: 22 of 37 flagged segments fell under the cutoff in one study
- Report words to know: junctional, segmental, axial
- Next step: have a vein specialist match your results to your symptoms
A vein ultrasound times how long blood flows backward through each segment of your leg veins, and a segment that runs past its limit gets flagged. Whether a flag leads to treatment depends on your symptoms and on which veins are involved.
What Venous Reflux Means in Your Legs
Your leg veins have tiny one-way valves inside them, small flaps that swing shut after each push of blood. When you walk, your calf muscles squeeze blood upward and each valve closes behind it so gravity can't pull the blood back down. When a valve stops closing all the way, some blood slips backward and pools. That backward slip is venous reflux.
It's behind a lot of the heavy, achy, swollen legs people write off as "just getting older," and it's a common driver of varicose veins. The part that surprises people is the timeline. Bulging veins are a late arrival, and the leak can start well before anything shows on the surface.
How the Scan Times the Backward Flow
A duplex ultrasound pairs a live picture of the vein with a reading of blood flow. There are no needles and no radiation, just a plastic probe and ultrasound gel, the same kind of probe used for ultrasounds in pregnancy.
| Step | What happens | What it tells us |
|---|---|---|
| Gel and probe | The technician moves the probe along your leg | Where each vein runs and how wide it is |
| Stand | You stand when you can, which gives the valves their real-life test | How the valves hold up against gravity |
| Squeeze and release | The calf is squeezed or a cuff is inflated, then let go | Whether blood falls backward when the squeeze ends |
| Time the flow | The screen shows any backward flow and the technician times it | How long each segment leaks |
Reflux can show up in a surface vein, a deep vein or a perforator, so the technician works through the leg segment by segment and times each one separately.
Standing changes the readings, and if your own scan was done lying down, that's worth mentioning to your specialist. The 2022 clinical practice guidelines for varicose veins, written by the Society for Vascular Surgery with the American Venous Forum and the American Vein and Lymphatic Society, call for scanning standing whenever possible. They review one study where 37 vein segments showed reflux longer than half a second with people lying down. When the same people stood, 22 of those segments (59%) came in under that cutoff.
At Beltline Health, the whole visit, consult, scan and a talk about your results, runs about 45 minutes to an hour. Our step-by-step guide to a vein evaluation covers the rest of the visit.
Reading the Numbers on Your Report
Reports differ from lab to lab, and yours may list each vein segment, how long blood flowed backward, and how wide the vein measures. Ask for a copy of your report so you can follow along. The cutoffs for calling a segment reflux come from those same guidelines:
| Vein segment | Backward flow that counts as reflux |
|---|---|
| Great and small saphenous veins and their accessory branches (the main surface veins) | Longer than 0.5 seconds (500 milliseconds) |
| Tibial and deep femoral veins | Longer than 0.5 seconds |
| Perforating veins (short connectors between deep and surface veins) | Longer than 0.5 seconds. In people with varicose veins, a perforator counts as a problem when it is also wider than 3.5 mm |
| Common femoral, femoral and popliteal veins (the large deep veins of the thigh and knee) | Longer than 1 second |
The same number can get a different verdict depending on the vein. Say your report shows 0.8 seconds of backward flow. In the great saphenous vein, that's past the 0.5-second cutoff, so the segment is flagged. In the femoral vein, 0.8 seconds is under the 1-second cutoff, so it isn't.
Those figures answer one question: is this segment leaking? Three words on your report describe the pattern:
| Word on your report | What it means |
|---|---|
| Junctional | Reflux limited to the spot where a surface vein joins a deep vein, at the groin or behind the knee |
| Segmental | Reflux in one portion of a surface or deep main vein |
| Axial | Backward flow all the way from the groin down to the calf |
The pattern tells your specialist where the leak starts and how far it runs, and that shapes the treatment conversation.
Vein width gets a lot of attention, but specialists caution against deciding on it alone. In one study, the width of the great saphenous vein didn't line up with people's own quality-of-life ratings.
Normal and Mild Results: How to Read the Words
A normal result means every checked segment stays under its cutoff, so nothing gets flagged. If your legs still bother you, tell your specialist, because the scan checks valves and your symptoms may have another source.
"Mild" is trickier, because reflux is defined by a cutoff and a segment either reaches it or it doesn't. If your report uses a word like "mild" or "moderate," ask what it's describing: the timing, the width of the vein, or how few segments are involved.
After the Numbers: Matching Results to Your Symptoms
A treatment decision draws on three things: the reflux on your report, your symptoms, and your anatomy. Your symptoms might be heaviness, aching, swelling, skin changes, or legs that wake you at 3 a.m. Your anatomy is which veins leak and in what pattern.
After your scan, we sit down with the map of your legs and go through which veins are working and which have given up, in plain English, before you leave the room.
That map also guides treatment. Treatments for a leaking vein, such as radiofrequency ablation or VenaSeal, are done in the office under ultrasound guidance. They typically take 30 to 60 minutes, and our treatment page describes minimal downtime. The scan that finds the leak also shows us which vein to treat.
A few questions worth bringing to any results discussion, whether it's with us or with another specialist:
- Which segments show reflux, and for how long?
- Is the pattern junctional, segmental or axial?
- Was I scanned standing?
- How do these findings line up with my symptoms?
- If treatment is an option, what are my choices, and what happens if I wait?
Get Your Legs Scanned and Explained
If your legs feel heavy or achy by the end of the day, a scan can show what's going on inside them. Our vein team can scan your legs in the office and go over the results with you in the same visit.
Frequently Asked Questions
What is venous reflux?
Venous reflux is blood flowing backward in a leg vein because a one-way valve isn't closing fully. The blood pools, which over time can cause heaviness, swelling and visible varicose veins. A vein ultrasound is the test that confirms it.
Do I need treatment if my ultrasound shows mild reflux?
Not automatically. The decision rests on your symptoms and on which veins are involved, and vein size alone can't settle it. If your legs feel heavy, ache or swell, a vein specialist can tell you whether the reflux explains that and what your options are. If you have no symptoms, ask what follow-up makes sense.
Can venous reflux be reversed?
Damaged valves generally don't heal on their own. Treatments such as radiofrequency ablation or VenaSeal close the leaking vein so blood reroutes through healthier ones, and results vary from person to person. Our guide to what treatment actually does for chronic venous insufficiency walks through the choices.
How does a vein evaluation at Beltline Health work?
We start with a consultation, then an in-office duplex ultrasound of your legs, then go over your results with you. Plan for about 45 minutes to an hour. Wear loose clothing, or change into the shorts we have on hand.
Medically Reviewed By: Charles Procter, Jr., MD, FACS
