Genes explain about half the variation in who develops dangerous vein clots
Deep vein thrombosis is a clot in a deep vein, usually in the leg or pelvis. Its real danger is travel: a fragment can pass through the heart and lodge in a lung artery. Surgery and long journeys raise the risk, but genes account for roughly 50 to 60 per cent of the variation between people.
Doctors group DVT and pulmonary embolism together as venous thromboembolism. About two-thirds of cases involve only a leg or pelvic clot, while a third involve the lungs, with or without a visible leg clot. Up to a quarter of pulmonary embolisms are thought to cause sudden death. Even when a clot is treated, the story is not always over: about 30 per cent of people have another episode within ten years, and the commonest long-term complication, post-thrombotic syndrome, brings heaviness, swelling, itching and sometimes ulcers.
For over a century the explanation rested on Virchow's triad: sluggish blood flow, blood that clots too readily, and damage to the vessel lining. Inflammation has since been shown to play a clear causal role too. Listed risks include recent surgery, older age, active cancer, obesity, infection, pregnancy and the weeks after birth, hormonal contraception, and long periods without moving, including long-haul travel. Among the inherited factors are having a blood type other than O and mutations such as factor V Leiden. Yet many people with several risk factors never develop a clot.
The typical signs are pain, swelling and redness in one leg, building over hours or days, though some clots cause no symptoms and 4 to 10 per cent occur in the arms. Most suspected cases are ruled out on examination, since cellulitis and a ruptured Baker's cyst can look very similar. Clinicians use scoring rules such as the Wells score and a D-dimer blood test to judge likelihood, and confirm with ultrasound. Researchers are now testing artificial intelligence for reading those scans; a 2025 review of eleven studies found promising accuracy but concluded AI should support rather than replace expert readers.
Risk climbs steeply with age: rare in children, it affects almost 1 per cent of people aged 85 and over each year. It is more common in men than women, and populations in Asia show rates of only 15 to 20 per cent of those in Western countries. Standard treatment is blood-thinning medication, and after low-risk surgery the main preventive step is getting patients walking early and often.
Source: Deep vein thrombosis
