Medicines for Factor V Leiden

What it is

Factor V Leiden is a common inherited variation in a gene involved in blood clotting, which makes the blood slightly more prone to forming clots (a "thrombophilia"). It is the most common inherited clotting tendency, particularly in people of European origin. Importantly, most people who carry it never have a blood clot, so it is not a disease in itself but a risk factor. It slightly increases the chance of clots forming in the deep veins (deep vein thrombosis, DVT) and travelling to the lungs (pulmonary embolism), especially when combined with other risk factors — such as surgery, long periods of immobility, long-haul travel, pregnancy, and the combined contraceptive pill or HRT. Inheriting the change from both parents (less common) carries a higher risk than from one. It is diagnosed with a blood test, usually done after a clot or when there is a strong family history.

How it is treated

Because most carriers never have problems, factor V Leiden usually needs no treatment in itself, and the focus is on awareness and reducing clot risk in higher-risk situations. People who carry it are advised on measures during higher-risk times — such as staying mobile and hydrated on long journeys, and taking precautions around surgery — and may be offered clot-preventing treatment (such as blood thinners) around particularly high-risk periods like major surgery or during and after pregnancy, decided individually. The combined contraceptive pill and HRT, which slightly raise clot risk, are considered carefully, and alternatives discussed where appropriate. If a person does have a clot, it is treated with anticoagulation as usual, and the presence of factor V Leiden may influence how long treatment continues. Family members may be tested where relevant. The reassuring message is that carrying factor V Leiden usually causes no problems, and its risks can be managed sensibly.