DVT and Blood Clots: A Swollen, Painful Leg You Shouldn't Ignore
A blood clot in a deep vein (DVT) usually starts in the leg — and can become life-threatening if it travels to the lungs. A clear guide to the warning signs, who's at risk, and why it's a medical emergency.
A blood clot forming in a deep vein — usually in the leg — is called a deep vein thrombosis (DVT), and it's one of those conditions that's important to recognise, because while the leg symptoms can seem manageable, a clot can break off and travel to the lungs, becoming life-threatening. The good news is that DVT is treatable, and knowing the warning signs means you act in time. This is a clear, plain-language guide to DVT and blood clots — the signs, the risks, and when it's an emergency.
What Is DVT?
DVT is a blood clot that forms in one of the deep veins, most often in the calf or thigh. The danger is twofold: the clot can partly block blood flow in the leg, and — more seriously — a piece can break off and travel through the bloodstream to the lungs, causing a pulmonary embolism (PE), which is a medical emergency. Recognising and treating DVT early helps prevent this.
Warning Signs of DVT (Usually One Leg)
DVT often affects just one leg — a new, unexplained swollen, painful calf should be checked promptly, not waited out.
Who's at Higher Risk?
- Long periods of immobility — long flights/journeys, bed rest, after surgery or injury
- Recent surgery or hospital stay
- Pregnancy and the weeks after childbirth
- Certain medicines (like some hormonal ones), smoking, obesity
- Cancer, some clotting conditions, or a past DVT/family history
- Increasing age
Reducing Your Risk
- On long journeys, move your legs, walk periodically, and stay hydrated
- After surgery, follow advice to get moving and any prescribed prevention
- Stay active generally, keep a healthy weight, and don't smoke
- If you're at higher risk, discuss prevention with your doctor (especially around surgery, travel, or pregnancy)
How It's Treated
DVT is diagnosed with tests (like an ultrasound scan and blood tests) and treated with blood-thinning medicines (anticoagulants) that stop the clot growing and prevent new ones while the body breaks it down, greatly reducing the risk of PE. Early treatment is effective — another reason not to delay getting a suspicious leg checked.
When to See a Doctor
See a doctor promptly for an unexplained swollen, painful, warm, or red leg (usually one side) — especially if you have risk factors like recent surgery, immobility, a long journey, or pregnancy. And treat the signs of a pulmonary embolism (sudden breathlessness, chest pain, coughing blood, feeling faint) as an immediate emergency — call 112/108. An online consultation can help you judge how urgently a leg symptom needs to be seen, but a suspected clot needs prompt in-person assessment. Acting quickly with DVT genuinely prevents a life-threatening complication. (See our guides on varicose veins, leg swelling, and symptoms you should never ignore.)