Symptoms of deep vein thrombosis
By Dr. Bahir Hadi — Consultant Surgeon, PhD
Symptoms of a Blood Clot in the Leg (DVT): When Should You Seek Urgent Medical Attention?
A blood clot in the leg - medically known as deep vein thrombosis (DVT) - is a serious condition where a blood clot forms in the deep veins, most often in the calf or thigh. The condition affects approximately 1 in 1,000 adults annually in Denmark and is dangerous because the clot can break loose and travel to the lungs (pulmonary embolism) [1]. Early recognition saves lives.
The Classic Symptoms
Classic DVT presents with:
- Swelling of one leg (rarely both) - often the entire calf or the whole leg
- Pain or tenderness in the calf, especially with movement and on touch
- Warmth and redness in the swollen area
- Taut, shiny skin and visible superficial veins
- A feeling of "heaviness" and cramps
- Often, the symptoms begin gradually over hours to days - not suddenly like a muscle injury
Up to 50% of DVT cases occur without classic symptoms and are only discovered when a pulmonary embolism develops [2]. Therefore, clinical suspicion is crucial.
Pulmonary Embolism - Call 112
If the blood clot breaks loose and travels to the lungs, a pulmonary embolism occurs, with symptoms including:
- Sudden shortness of breath, often without exertion
- Chest pain, often worse on deep inspiration
- Cough, possibly with bloody sputum
- Rapid pulse (> 100 beats per minute)
- Fainting or a sudden drop in blood pressure
- Anxiety and a feeling that "something is wrong"
If you experience these symptoms - call 112 immediately. A pulmonary embolism is a life-threatening medical emergency.
Wells Score: Risk Assessment
Doctors often use the Wells score for DVT to assess the probability [3]:
| Criterion | Points |
|---|---|
| Active cancer | 1 |
| Paralysis or leg in a plaster cast | 1 |
| Immobilisation > 3 days / surgery < 4 weeks ago | 1 |
| Localised tenderness along the deep venous system | 1 |
| Swelling of the entire leg | 1 |
| Calf swelling > 3 cm larger than the other leg | 1 |
| Pitting oedema (only) on the affected leg | 1 |
| Previous DVT | 1 |
| Visible superficial veins (non-varicose) | 1 |
| An alternative diagnosis is at least as likely | -2 |
≥ 2 points = DVT likely → urgent D-dimer test + ultrasound scan. < 2 points = DVT unlikely → D-dimer test as the first step.
Risk Factors
- Immobilisation: long-haul flights, bed rest, plaster casts
- Recent surgery (especially hip/knee, abdominal)
- Cancer and cancer treatment
- Pregnancy and the postpartum period (5-6 × increased risk)
- Contraceptive pills, hormone therapy
- Previous DVT
- Hereditary thrombophilia (Factor V Leiden, protein C/S deficiency)
- Obesity and smoking
- Varicose veins and venous insufficiency increase the risk, particularly for superficial thrombophlebitis, which develops into DVT in 6-25% of cases [4]
Conditions Mistaken for DVT
DVT is often mistaken for:
- Muscle injury: occurs suddenly during activity, often with a "popping" or "snapping" sensation
- Calf cramps: short-lived, resolve on their own - see cramps in the calf
- Ruptured Baker's cyst: sudden calf pain, often in someone with a known knee problem
- Cellulitis/erysipelas: redness and fever, but more often well-demarcated
- Chronic venous insufficiency: gradual swelling, usually affecting both legs
If in doubt: see a doctor the same day - DVT is a diagnosis of exclusion that requires a D-dimer test and an ultrasound scan.
Treatment
DVT is treated with anticoagulation (blood-thinning medication) for at least 3 months [5]:
- DOACs (apixaban, rivaroxaban) are the first-choice treatment for most people
- LMWH (low-molecular-weight heparin) for 5 days plus warfarin is an alternative
- LMWH alone is used for patients with cancer, during pregnancy, or with severe kidney failure
The duration of treatment depends on the cause, risk of recurrence, and bleeding risk. For a provoked DVT (e.g., after surgery), treatment is often for 3 months; for an unprovoked or cancer-associated DVT, it is longer - often lifelong.
Post-Thrombotic Syndrome - The Long-Term Complication
Up to 20-50% of DVT patients develop post-thrombotic syndrome: chronic swelling, heaviness, pain, and skin changes in the affected leg [6]. This is effectively a secondary chronic venous insufficiency with the same spectrum of complications as primary varicose veins.
Wearing a Class 2 compression stocking for at least 2 years after a DVT significantly reduces the risk.
****
| Symptom | Action |
|---|---|
| One-sided swelling + calf pain | Contact a doctor urgently the same day |
| Pain + shortness of breath + chest pain | Call 112 |
| Both legs swollen, improves overnight | Get assessed for venous insufficiency |
| Tender, red, hard vein | Suspected thrombophlebitis |
If you have had a DVT, you should be assessed for chronic venous disease by a specialist consultant in vascular surgery.
References
- Heit JA. Epidemiology of venous thromboembolism. Nat Rev Cardiol 2015;12(8):464-74.
- Cohen AT, et al. Venous thromboembolism (VTE) in Europe. Thromb Haemost 2007;98(4):756-64.
- Wells PS, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med 2003;349(13):1227-35.
- Decousus H, et al. Superficial venous thrombosis and venous thromboembolism: a large, prospective epidemiologic study. Ann Intern Med 2010;152(4):218-24.
- Stevens SM, et al. Antithrombotic therapy for VTE disease: CHEST guideline 2021. Chest 2021;160(6):e545-e608.
- Kahn SR, et al. The post-thrombotic syndrome: evidence-based prevention, diagnosis and treatment strategies. Lancet 2014;383(9920):880-8.