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Deep Vein Thrombosis (DVT)

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 4 minutes read

A deep vein thrombosis (DVT) is a blood clot that develops in a large vein, usually in the lower leg, and requires treatment to ease symptoms and prevent clots from spreading to other areas in the body.

A pulmonary embolism (PE) is the most serious complication, where part of the DVT breaks off and a clot lodges in one of the blood vessels going to the lungs, blocking the blood supply. This can cause difficulty in breathing and collapse – it's a life-threatening condition that requires immediate medical attention.

It’s believed that around 900,000 people in the US have a DVT or PE every year.

What causes a DVT?

You may have other medical conditions that make your blood more likely to clot. These include pregnancy, and for up to six weeks after your baby's delivery, and cancer, especially if you are receiving treatment or have had treatment within the previous six months.

Periods of immobility or illness can put you at higher risk, such as a long operation in the previous four weeks, or illness or injury that has kept you in bed for more than three days. COVID-19 puts you at a higher risk of blood clots, although PEs are more likely to occur than DVTs in these cases.

If you are admitted to the hospital for any reason, your medical or surgical team will assess your risk, weighing up the risk of blood clots versus increasing your bleeding risk and may give anticoagulant (blood-thinning) medication to reduce your risk of developing DVTs.

Other factors can contribute to your risk, such as dehydration, smoking, obesity, flights or travel for more than three hours, those on hormone replacement therapy (HRT) or the contraceptive pill, a previous DVT, certain clotting disorders, and those aged over 60. A DVT is not the same as varicose veins, although they put you at slightly higher risk.

It helps to ensure you stay well-hydrated and mobile where able. Make sure you keep to a healthy weight and stay active with regular exercise. For long-haul flights, it’s not recommended that you take aspirin (unless you are prescribed this for another reason) but you should move around and stretch your legs regularly. You can buy compression stockings that may reduce your DVT risk – your pharmacist will help you find the right size.

When should I suspect a DVT?

A DVT is suspected if your leg develops a hard, red area that’s warm and tender when squeezed, and the calf or thigh will be obviously swollen compared to the other leg. You may feel a throbbing or cramping pain, especially when you walk on that leg.

If you have any of these symptoms and you also have chest pain and shortness of breath, this could be a DVT and PE - this requires immediate medical attention and you should call an ambulance or get to your local Emergency Department without delay.

When should I see my doctor?

See your doctor urgently if you have signs of a DVT, whether or not you have risk factors. Alternatively, you can call 911 or visit an urgent care center or walk-in center. The doctor will ask about your symptoms and any relevant medical history. They will take your vital signs and examine your leg. They may measure your calf and compare it to the other one.

They use a scoring system called the Well’s score, where certain symptoms, signs and risk factors get points that make a DVT more or less likely. If your score makes a DVT likely, you will be referred to the hospital medical team, where they may do blood tests (particularly one called a D-dimer test) and an ultrasound scan of the vessels called a venous Doppler, to confirm if a DVT is present. If there’s any delay in investigations, they may start treatment ahead of time.

How is it treated?

Treatment is with an anticoagulant, which thins the blood to break down the clot and prevent new clots. You may be given heparin injections until investigations have confirmed a DVT.

They will be replaced with anticoagulant tablets for you to take at home, and treatment usually continues for at least three months. Tablets may be warfarin - which requires regular blood tests - or a newer family of anticoagulants called direct oral anticoagulants (DOACs) such as rivaroxaban, dabigatran, edoxaban or apixaban, which do not. There are different protocols for different hospitals.

Your medical team will consider likely causes and try to minimize risks to avoid a DVT or PE in the future. You should avoid flights for at least two weeks after you start anticoagulant tablets. Once you’re on treatment, you should make sure you walk regularly and keep your affected leg elevated when seated, to help disperse the clot.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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