Thrombophilia

Also called Sticky blood, Factor V Leiden, Inherited clotting disorder

A tendency to clot. Testing is far less useful than people expect, and a positive result rarely changes what is done.

What it is

An increased tendency to form blood clots, either inherited or acquired.

The commonest inherited form is factor V Leiden, carried by around 5 per cent of people of European ancestry. Most carriers never have a clot in their lives. Others include prothrombin gene mutation and deficiencies of protein C, protein S and antithrombin, which are rarer and carry higher risk. The most important acquired form is antiphospholipid syndrome.

The central point is counter-intuitive: **testing is much less useful than people assume**, and it is frequently requested and rarely helpful. A positive result usually does not change treatment, because the decision on how long to anticoagulate depends far more on whether the clot was provoked by something temporary such as surgery, and on bleeding risk. Testing can also cause harm: false reassurance from a negative result, anxiety, and difficulty getting insurance.

Testing is worth doing in specific situations: suspected antiphospholipid syndrome, unusual sites of clot, a strong family history in a young person, and sometimes for family planning advice.

What matters far more than a gene test is recognising the situations that provoke clots and taking prevention seriously: surgery, hospital admission, immobility, long travel, pregnancy, and combined hormonal contraception or HRT.

Signs you might notice

Thrombophilia itself has no symptoms. What matters is the clots.

Deep vein thrombosis: a swollen, painful, warm calf or thigh.

Pulmonary embolism: sudden breathlessness, chest pain worse on breathing in, coughing blood, collapse.

Clots in unusual places: severe abdominal pain, or a severe persistent headache with visual changes, which can indicate a clot in a vein draining the brain.

Recurrent miscarriage or late pregnancy loss, which points at antiphospholipid syndrome.

999 for sudden breathlessness, chest pain or stroke-like symptoms.

Urgent: a swollen painful calf.

Ask about testing where clots occur young, recur without provocation, run strongly in the family, or occur in unusual sites.

How it can affect day-to-day life

Prevention at the risky moments is the whole practical content: telling every hospital, asking about clot risk assessment on admission, using stockings and injections when offered, moving and hydrating on long journeys, and getting up regularly during immobility.

Combined hormonal contraception and standard oral HRT raise clot risk, and in someone with a known thrombophilia or a previous clot, alternatives exist and should be discussed rather than the topic being avoided.

Pregnancy raises risk substantially, and women with a history need a plan made before conceiving, often involving heparin injections through pregnancy and for six weeks afterwards.

Family members frequently want testing after a relative's clot. The honest answer is that for the common mutations it rarely changes anything, and that knowing the risky situations matters more.

Anticoagulation, when used, brings bleeding risk and the need to tell every clinician including the dentist.

Supporting someone well

Do not push for testing without a clear reason; ask what the result would change.

Do ask about testing for antiphospholipid syndrome after recurrent miscarriage, a young stroke, or an unusual clot.

Tell every hospital and clinician about any previous clot or known thrombophilia.

Ask about clot risk assessment and prevention on every hospital admission.

On long journeys, move regularly, keep hydrated, and consider stockings.

Discuss contraception and HRT openly rather than avoiding it; alternatives exist.

Plan pregnancy in advance with a haematologist or obstetrician.

Learn the symptoms of clots and act on them the same day.

While anticoagulated, never stop without advice and tell the dentist.

Where to get help

A GP practice for referral to haematology where testing is indicated.

999 for breathlessness, chest pain or stroke symptoms; same-day for a swollen painful calf.

Thrombosis UK run a support network and publish clear guidance on prevention.