Prothrombin and DVT

You wake up one morning with a pain in your leg, trying to think back as to what you did the previous day to cause it.  Then you notice that your leg is a little swollen and warm…  Oh no, this could be the signs of a blood clot in your leg! [ref]

Deep vein thrombosis (DVT) occurs when you have a blood clot in one of the larger veins of your arm or leg. This blood clot can then break free and travel to the lungs (pulmonary embolism). A blood clot that blocks the blood supply to the lungs is, obviously, a very serious problem.

Blood clots can occur for a variety of reasons such as injury, surgery, and certain medications (chemo, birth control, etc.). Blood clots can also occur when sitting too long if the blood pools in the lower parts of your legs.

Venous thromboembolism occurs at a rate of 1 in 1,000 adults per year in the US.  Venous thromboembolism is a term that encompasses both deep venous thrombosis and pulmonary embolisms.[ref]

At the top of the list of risk factors for DVTs is always ‘a family history’ of blood clots. Genetics (heredity) is a large factor in who is more likely to get a blood clot.

Where else is blood clotting a problem? Ischemic strokes. This is the type of stroke that causes decreased oxygen due to lack of blood flow — usually due to a blood clot blocking the artery.

One genetic risk factor for DVT and, in certain circumstances, stroke is the G20210A variant of the prothrombin F2 gene.

About 2% of Caucasians carry the G20210A variant, but it is much less common in Asians, Africans, and Native Americans. A meta-analysis of the data from a bunch of studies found that carrying the G20210A variant increased the risk of thromboembolism by 2.6 to 4.4-fold (depending on the location of the clot). It is rare to carry two copies of the G20210A, but the statistical odds of DVT for those who are homozygous is higher. The risk of DVT is also greatly increased in carriers of both G20210A and the factor V Leiden (check it here) variants.[ref]

The studies on stroke risk for the F2 G20210A give a variety of results as to the increase in risk. A meta-analysis found that the G20210A variant increased the risk of ischemic stroke by almost 2-fold, but this may be a little misleading when looking at the whole population. For people who have a patent foramen ovale (PFO) – hole in the heart – the risk of stroke for those with the G20210A variant was almost 4X.[ref]  About 25% of the population has a PFO (hole in the heart), but most people don’t even know that they have it.[ref]  So a lot of the increase in risk for stroke from the G20210A variant may only be in people with a patent foramen ovale.

The G20210A variant also increases the risk of miscarriage (due to a blood clot in the placenta)[ref] and increases the risk of DVT in pregnancy a little [ref]

Check your 23andMe data for i3002432 (rs1799963, G20210A):

  • A/A: large increase in the risk of blood clots, increased risk of stroke with PFO
  • A/G: increased risk of blood clots, increased risk of stroke with PFO
  • G/G: normal


You can reduce your risk of DVT by not sitting for long periods of time.  Get up, move around. Newer activity monitors  — like the Fitbit or Oura ring – can detect when you have been sitting for an hour and prompt you to get up and move.  Or you can just set your timer on your phone to give you an alert every hour or so to remind you.

Stuck on a plane or in a meeting? Get your legs moving as much as possible — do ankle circles or just raise your heels up and down.

Talk with your doctor about whether low dose aspirin would be of any benefit for you. The research on the topic shows various results depending on the circumstances (pregnancy, age, previous dvt, etc).  A long-term clinical trial found that low-dose aspirin had little effect (~5% reduction in risk) for women over age 45. [ref]

Vitamin E has been shown in studies to reduce the risk of DVT.[ref] But for some people, vitamin E may not be the right option. Read these two articles first:  Vitamin E and increased cancer risk.  Vitamin E and Inflammation.

More to read:

Factor V Leiden


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