DVT (Deep Vein Thrombosis)

A deep vein thrombosis is a blood clot in a deep vein, usually in the calf or thigh. It matters because part of the clot can break off and travel to the lungs, a pulmonary embolism, which can be life-threatening. Estrogen raises the risk; so does surgery.

Where you'll meet it

In the risks section of any conversation about estrogen, on surgical consent forms, and in the question of whether to pause hormones before an operation. You will also see the pair abbreviated together as VTE (venous thromboembolism), which covers both a DVT and a pulmonary embolism (PE).

Why estrogen matters

Estrogen makes the blood a little more prone to clotting, because it changes the clotting proteins the liver makes. How much depends on the type and route. The old synthetic estrogen, ethinylestradiol, found in most contraceptive pills, carried a clearly higher risk and is no longer recommended for trans women. Oral estradiol passes through the liver first, which raises clotting factors more than estradiol through the skin (transdermal) or by injection. For someone with other risk factors, that is often why a prescriber suggests patches or gel.

For a young, healthy non-smoker on estradiol, the absolute risk is low. It is still the most important serious risk of feminizing hormones, which is why feminizing risks leads with it.

Testosterone and clots

Testosterone does not act on clotting proteins the way oral estrogen does, but it raises hematocrit, the share of the blood made of red cells. Thicker blood is a clot risk of its own when hematocrit runs high, which is one reason it is watched on masculinizing hormones.

What adds to the risk

Smoking is the big one. Others are age, being overweight, being inactive for long periods, long-haul flights, a personal or family history of clots, some inherited clotting conditions, and surgery. Several of those tend to stack up at once when people travel abroad for an operation: a long flight in, hours on the operating table, days in bed, and a long flight home. That is why surgeons ask about hormones well before the date, and why I tell patients flying to Bangkok to ask about the flight home as well as the operation.

How it's found and treated

A suspected DVT is usually checked with an ultrasound scan of the leg, often after a blood test called a D-dimer. A suspected PE is usually confirmed with a scan of the chest. Treatment is blood-thinning medicine (anticoagulants), for months rather than days. Whether you can carry on with hormones afterwards is a decision for your prescriber, often with a haematologist; many people do continue, often on a transdermal form.

Signs to know

Pain, swelling, warmth or redness in one leg, usually the calf. Sudden breathlessness, chest pain that is worse on breathing in, a racing heart, or coughing up blood are signs of a clot in the lung, and need emergency care straight away. Tell whoever sees you that you take hormones and which ones.

Common questions

Patches mean no risk. Lower is not zero, and the other risk factors still count.

Stopping estrogen before surgery is always safest. Stopping has costs of its own, and many surgeons now ask most patients to continue, managing clot risk with stockings, calf pumps, blood-thinning injections and early walking. Hormones and surgery covers it. Do not stop on your own.

What to ask

Given my age, weight, smoking and family history, which form of estrogen do you recommend? Do I need to be tested for an inherited clotting condition? What help can I get to stop smoking? And, before any operation, what does my surgeon want me to do with my hormones, in writing?

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