World Thrombosis Day 2026: DVT, PE and Blood Clot Warning Signs
Today, 13 October, is World Thrombosis Day. Thrombosis means blood clotting, and clotting itself is not a bad thing. The problem is a clot that forms where it should not, inside a blood vessel. In this short video Dr Andrew Choong explains the difference, and the warning signs that should send you to a doctor.
Sudden breathlessness, chest pain, coughing blood or collapse may indicate a pulmonary embolism. This is an emergency: call 995 in Singapore. A newly swollen, painful leg needs medical assessment the same day.
Is Blood Clotting Always Dangerous?
No. Clotting is essential. If you cut yourself or have an injury, clotting is what stops you bleeding. Without it, a small wound could be life-threatening.
The danger starts when a clot forms inside a blood vessel and blocks the flow of blood, or when part of it breaks away and lodges somewhere else. The World Thrombosis Day campaign estimates that one in four deaths worldwide involves a clot of this kind. The short video on why blood clots form explains the three conditions that make this more likely.
What Happens When a Clot Forms in an Artery?
Arteries carry oxygen-rich blood from the heart to the rest of the body. A clot in an artery can cut off that supply:
Brain: a blocked artery can cause a stroke. See carotid artery disease.
Heart: a blocked coronary artery can cause a heart attack.
Leg: a blocked leg artery can cause limb-threatening ischaemia, where the leg or foot does not receive enough blood to survive. See peripheral arterial disease.
These are the same problem in three places, which is the subject of the World Heart Day article on heart attack, brain attack and leg attack.
What Is a Deep Vein Thrombosis?
The clot most people need to understand on World Thrombosis Day is a venous clot. A deep vein thrombosis (DVT) is a clot in the deep veins, usually of the leg.
The leg may become swollen, painful, red, warm or tight, often on one side only. That one-sidedness is the clue. Both legs swelling together usually has another cause; one calf or one whole leg swelling over hours or days needs to be checked. A DVT is confirmed or excluded with a duplex ultrasound scan, which is painless and uses no radiation.
Why Is a Pulmonary Embolism So Serious?
The real danger of a DVT is that part of the clot can break off and travel through the heart to the lungs. That is a pulmonary embolism (PE). It can cause sudden breathlessness, chest pain, collapse or even death.
A pulmonary embolism can occur without any warning from the leg, and a small one can be followed by a larger one. This is why a suspected DVT is treated as urgent. The video on DVT and pulmonary embolism warning signs goes through the symptoms in more detail.
Who Should Be Particularly Alert?
Do not ignore one-sided leg swelling, especially:
after surgery or a stay in hospital
after a long flight or long road journey
after a period of prolonged immobility, such as bed rest or a leg in a cast
if you have cancer or are having cancer treatment
during pregnancy and in the weeks after delivery
if you have had a clot before
Many venous clots are linked to a hospital stay, and much of that risk is preventable. Our earlier World Thrombosis Day article, Blood-Clot Prevention Must Keep Pace With Hospital Care, explains the two questions worth asking whenever you or a relative is admitted.
Know the Signs and Get Checked Early
Blood clotting is normal. Abnormal blood clotting can be deadly. Most DVTs are treated with blood-thinning medicines, and selected patients with an extensive clot may be considered for clot removal; the DVT treatment page and the video on the DVT treatment window explain why timing matters. Swelling, heaviness or skin changes that persist months after a clot can also be assessed; see post-thrombotic syndrome.
For a swollen or painful leg, a previous clot, or a planned second opinion, contact Andrew Choong Vascular Surgery at Mount Elizabeth Novena Specialist Centre. The visit preparation guide lists what to bring, and patients travelling from overseas can read the international patients page. You can also watch the World Thrombosis Day video on its own page, or browse all blood clot videos.