Quick answer. Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the calf or thigh. Warning signs include new swelling, pain, warmth or redness in one leg. DVT is a medical emergency when part of the clot breaks off and travels to the lungs, causing a pulmonary embolism (PE), which can be life-threatening. Sudden breathlessness, chest pain (especially on breathing in), coughing up blood or fainting needs emergency care, call 995 or go to the nearest A&E immediately. Risk factors include prolonged immobility such as long flights, recent surgery, cancer, pregnancy and inherited clotting tendencies. DVT is treated with anticoagulant (blood-thinning) medication. This is general information, not medical advice.
Deep vein thrombosis (DVT) happens when a blood clot forms in one of the deep veins of the leg or pelvis. On its own it can cause leg swelling and pain, but the most serious danger is that a piece of the clot can break away and lodge in the lungs, a pulmonary embolism (PE), which is potentially fatal. Because of this, DVT and PE are treated urgently. This guide explains the risk factors (including long-haul flights and immobility), the red-flag symptoms, why PE is an emergency, and how DVT is treated with anticoagulation in Singapore.
At a glance
| Concern | What you may notice | What to do |
|---|---|---|
| Possible DVT | Swelling, pain, warmth or redness in one leg, often the calf | See a doctor urgently the same day for assessment |
| Possible pulmonary embolism (PE) | Sudden breathlessness, chest pain worse on breathing in, coughing blood, fainting, racing heart | Call 995 or go to A&E immediately |
| Higher-risk situations | Long flight or immobility, recent surgery, cancer, pregnancy, clotting disorder | Take prevention steps; seek care early if symptoms appear |
What is DVT and why does it matter?
A deep vein thrombosis is a clot that forms in the deep veins, most commonly in the lower leg or thigh. The serious concern is that the clot can break loose and travel through the bloodstream to the lungs, blocking an artery there. This is called a pulmonary embolism, and a large PE can be life-threatening. Together, DVT and PE are known as venous thromboembolism (VTE). Recognising DVT early and starting treatment promptly greatly reduces the risk of a dangerous embolism.
Risk factors, including long flights and immobility
Clots are more likely when blood flow slows, the vein wall is injured, or the blood clots more easily. Common risk factors include prolonged immobility such as long-haul flights or long car journeys, recent major surgery (especially hip, knee or abdominal), serious injury, hospital admission, cancer and its treatment, pregnancy and the weeks after delivery, hormonal medications (some contraceptive pills and hormone therapy), obesity, increasing age, and inherited clotting tendencies such as factor V Leiden. A personal or family history of clots also raises risk. For very short flights the risk is small, but it rises with travel duration and when other risk factors are present.
Red-flag leg symptoms
Suspect DVT if you develop, usually in one leg, new swelling, pain or tenderness (often starting in the calf), warmth, or redness or discolouration of the skin. The leg may feel heavy or ache, especially when standing or walking. These symptoms warrant urgent same-day medical assessment. A doctor can arrange a duplex ultrasound and a blood test (D-dimer) to confirm or rule out a clot. Do not massage the affected leg.
Pulmonary embolism is an emergency
A pulmonary embolism can occur with or without obvious leg symptoms. Seek emergency care immediately, call 995 or go to the nearest A&E, if you experience sudden shortness of breath, chest pain that is sharp or worse when you breathe in, coughing up blood, a fast or irregular heartbeat, light-headedness or fainting. PE can be fatal, and rapid treatment saves lives. Do not wait to see if symptoms settle.
How DVT is treated
The mainstay of treatment is anticoagulation (blood thinners), which stops existing clots from enlarging and prevents new ones, while the body gradually breaks the clot down. Options include direct oral anticoagulants (DOACs) and, in some situations, injectable heparin or warfarin. Treatment usually continues for at least three months, and sometimes longer or indefinitely if the risk of recurrence is high. In selected severe cases, clot-dissolving therapy, catheter procedures or a vena cava filter may be considered. Your doctor will weigh the benefits against bleeding risks and advise on duration.
Reducing your risk
On long journeys, move your legs and walk regularly, do calf exercises while seated, stay hydrated, and consider graduated compression stockings if you are at higher risk. Around surgery or hospital stays, follow the prevention plan your care team gives you, which may include early mobilisation, compression devices or preventive anticoagulation. If you have had a DVT or PE before, or have a strong family history, discuss your individual risk and any precautions with your doctor before long travel or surgery.
Living with anticoagulant treatment
If you are started on blood-thinning medication after a DVT, a few practical habits help you take it safely. Take the medicine exactly as prescribed and at the same time each day, and do not stop early even if your leg feels better, as the clot is still being managed. Because anticoagulants increase the risk of bleeding, tell any doctor, dentist or pharmacist that you are taking them before procedures, and seek medical advice for unusual bruising, blood in the urine or stool, or bleeding that does not stop. Some medicines, supplements and, for warfarin, certain foods can interact with treatment, so check before starting anything new. Carry a note or card stating which anticoagulant you take.
Special situations
Pregnancy and the weeks after delivery raise the risk of clots, and not all blood thinners are suitable during this time, so DVT in pregnancy is managed closely by your doctor. People with cancer, recent major surgery or a previous clot may need a longer or tailored course of treatment. If you have had a DVT or PE before, discuss your individual risk with your doctor well ahead of long-haul travel or any planned operation, so that preventive measures can be arranged.
Common questions
How long will I need to take blood thinners?
Treatment usually lasts at least three months, but the exact duration depends on what caused the clot and your risk of it happening again. Some people continue for longer or indefinitely; your doctor will weigh the benefits against bleeding risk.
Can I exercise after a DVT?
Gentle movement and walking are generally encouraged once treatment has started, as they support circulation. Avoid massaging the affected leg, and follow your doctor’s advice on activity.
Related guides
- Best Vascular & Vein Clinics in Singapore — our editorial shortlist
- Varicose veins
- PAD
- Leg swelling and spider veins
Sources
- HealthHub Singapore
- SingHealth – Symptoms and Treatments
- CDC Yellow Book – DVT and Pulmonary Embolism
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