What Is a DVT? Deep Vein Thrombosis Explained

Deep vein thrombosis, or DVT, is a blood clot in a deep vein. It most often affects the leg or pelvis, although it can also develop in an arm. Deep veins carry blood back towards the heart, so a clot can obstruct that return flow.

In the third instalment of my Blood Clot Awareness Month series, I explain why DVT deserves attention: it can cause immediate symptoms, sometimes lead to a pulmonary embolism, and leave longer-term problems in the affected leg. Recognising a possible clot is the first step towards getting it assessed.

What does a DVT feel or look like?

Possible signs include new swelling, pain or tenderness, warmth, and a change in skin colour, usually affecting one leg. The discomfort may involve the calf or thigh. An arm DVT can produce similar symptoms in the arm.

These signs do not prove that a clot is present. Muscle injuries, infections and other conditions can look similar, and some DVTs cause few or no obvious symptoms. Comparing one leg with the other can reveal a change, but a home examination cannot confirm or exclude DVT.

New, unexplained one-sided swelling or pain warrants urgent medical assessment. Do not wait for symptoms to become severe before seeking advice.

Why can a leg clot affect the lungs?

Part of a DVT can break off and travel through the bloodstream to the pulmonary arteries in the lungs. This is called a pulmonary embolism, or PE. It can interfere with oxygen exchange and strain the heart.

Sudden breathlessness, chest pain, coughing up blood or fainting need emergency assessment. For these possible pulmonary embolism symptoms, call 995 in Singapore; do not wait for symptoms to worsen. A routine vascular appointment is not the appropriate first step when PE is suspected.

DVT and PE are related conditions collectively called venous thromboembolism, or VTE. Not every DVT causes PE, but the possibility is one reason early diagnosis and treatment matter.

Can DVT threaten the leg itself?

Rarely, a very extensive DVT can severely obstruct the veins draining the leg. The leg may become dramatically swollen, very painful and discoloured. This severe condition, known as phlegmasia, can threaten the limb and requires emergency specialist care.

This is different from the more usual presentation of DVT, but it illustrates why a rapidly worsening, painful swollen leg should not be managed by waiting at home. Emergency assessment is particularly important if the limb becomes blue, cold or numb.

What is post-thrombotic syndrome?

After a DVT, residual obstruction or damage to the vein valves can make it harder for blood to return efficiently. Some people develop post-thrombotic syndrome, with persistent swelling, aching, heaviness or skin changes. In more severe cases, a venous ulcer can develop.

These problems can affect daily life even after the immediate clot has been treated. They do not happen to everyone. Follow-up allows ongoing symptoms to be assessed and a suitable management plan to be discussed.

Who is more likely to develop DVT?

Risk factors include recent surgery or hospitalisation, reduced mobility, a previous clot, active cancer, pregnancy and the period after childbirth. Certain hormone medicines and inherited clotting tendencies can also increase risk.

Long journeys can contribute through prolonged sitting, particularly when other risk factors are present. Sometimes a DVT develops without an obvious trigger. The clinical history helps determine both the likely cause and how best to reduce future risk.

How is DVT assessed and treated?

A clinician considers the symptoms, examination and risk factors. An ultrasound scan is commonly used to look for a clot in the deep veins; blood tests may form part of the assessment in selected circumstances.

Anticoagulant medicines are the main treatment for most DVTs. They help prevent the clot growing and reduce the chance of further clots while the body's natural processes work on the existing clot. Treatment duration depends on the individual situation.

Selected patients with extensive, severely symptomatic clots may be considered for catheter-based treatment. This is not necessary for every DVT. Decisions balance potential benefit against bleeding and procedural risks.

You can read more about DVT assessment and treatment or contact my Singapore clinic at Mount Elizabeth Novena Specialist Centre, #09-22, 38 Irrawaddy Road, Singapore 329563 for non-emergency advice and follow-up.

This article provides general education and does not replace an individual medical assessment.