Leg swelling (oedema) has many causes, ranging from benign and self-limiting to serious and requiring urgent treatment. The key clinical distinction is between unilateral swelling (one leg only) and bilateral swelling (both legs).
| Type | Common causes |
|---|---|
| Unilateral (one leg) | Deep vein thrombosis (DVT), cellulitis, Baker's cyst rupture, lymphoedema, muscle injury |
| Bilateral (both legs) | Heart failure, chronic venous insufficiency, hypoalbuminaemia, lymphoedema, medication side effects |
Unilateral leg swelling — particularly when associated with calf pain, warmth, or redness — should always be investigated for DVT. DVT is a blood clot in the deep veins of the leg, and it carries the risk of pulmonary embolism (PE) if the clot breaks off and travels to the lungs.
The classic symptoms of DVT include:
DVT can also be entirely asymptomatic — present without any symptoms — which is why it is sometimes only discovered incidentally on imaging performed for another reason.
Seek emergency care immediately if you have leg swelling alongside sudden breathlessness, chest pain, or coughing up blood. These symptoms may indicate a pulmonary embolism, which is a medical emergency. Call 999.
DVT risk is increased by:
If you have unilateral leg swelling with any of the symptoms described above, a DVT ultrasound scan is the appropriate first investigation. It is the gold-standard test for DVT, recommended by NICE as the first-line diagnostic investigation.
At Sonoworld, same-day DVT scans are available. A duplex ultrasound of the leg veins takes approximately 30 minutes, and you will receive verbal results immediately after the scan.
If a DVT is confirmed, the report will clearly state this so you can attend your GP or A&E for anticoagulation treatment without delay.
The most common scenario we see is a patient who has returned from a long-haul flight with a swollen, painful calf. Their GP has advised them to "keep an eye on it" and return in a week if it does not improve. A same-day DVT scan at Sonoworld provides an answer within the hour — either confirming the DVT and enabling prompt anticoagulation, or excluding it and providing genuine reassurance. A week's delay in diagnosing a DVT is not clinically acceptable; the risk of pulmonary embolism during that week is real.
Yes. Long-haul flights are a recognised risk factor for DVT (sometimes called "economy class syndrome"). If your leg swelling after a flight is unilateral and associated with pain or warmth, you should get a DVT scan promptly.
No. The scan is entirely painless. See our DVT scan Q&A for a full guide to what happens during the scan.
If a DVT is confirmed, you should attend your GP or A&E with your scan report. You will be prescribed anticoagulation medication (blood thinners) to prevent the clot from extending and to reduce the risk of pulmonary embolism.
Sonoworld is registered with the Care Quality Commission (CQC). Our sonographers are registered with HCPC and are members of BMUS. All scans are performed at our Marylebone clinic: 29 Weymouth Street, London W1G 7DB.
Same-day and next-day appointments available at our Marylebone clinic. Instant verbal results. Written report within 24 hours. No GP referral required.
Price: £235
Or call us on 020 7486 1991
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