Medical Matters > Blood: Clots (Thrombosis)

ME Essential Summer 2022


Are people with ME more likely to develop blood clots? I ask because I am due to go into hospital for some quite major surgery and will be fairly immobile for some time afterwards. The hospital consultant has queried whether people with ME are at increased risk from developing blood clots. I also understand that blood-thinning drugs are sometimes given after an operation to people who have risk factors for developing blood clots.


A blood clot (or thrombosis) is a serious medical problem whereby the inside of a vein becomes blocked. One well-known example is a deep vein thrombosis (DVT) in the leg – which causes pain, swelling, redness and warmth. In addition to swelling of the area that is supplied by the vein, there is a risk that a small portion of the clot (an embolus) can break off and go to the lungs (where it can cause a pulmonary embolism/chest pain and breathlessness) or the brain (where it can cause a stroke).

Blood clots represent a medical emergency and require treatment with either ‘blood thinning' drugs (anticoagulants) or surgical removal of the actual clot (a thrombectomy).

The simple answer to your question is that there is no evidence that any aspects of what we know about the underlying disease process in ME/CFS – i.e., abnormalities involving muscle, brain, cardiac function or immune system dysfunction – make people more likely to develop blood clots. And we don’t have any patient feedback to indicate that blood clots are more common in people with ME/CFS. However, there are three risk factors for blood clots that can be relevant to people who have ME/CFS:

  • First is physical inactivity – which is obviously going to be very relevant in people who are more severely affected and are partially or totally bed-bound.
  • Second is being overweight – which can occur in ME/CFS.
  • Third is the fact that diseases that are linked to inflammation – examples being rheumatoid arthritis and inflammatory bowel disease – increase the risk of blood clot formation.

Other risk factors include smoking, a past history of having a blood clot, some types of hormone replacement therapy, the contraceptive pill, and pregnancy. As far as any risk pertaining to surgery is concerned, this will depend on individual circumstances and what risk factors are present (especially immobility) and how major the surgery is going to be in relation to post-operative immobility. If the risk is considered to be significant it may then be appropriate, as is obviously being discussed in your case, to take a blood thinning drug to reduce the risk.

See also: Blood Test: Platelet Count.


Information provided by The ME Association should not be construed as medical advice. Don't assume any new or worsened symptoms are simply the result of having ME/CFS or Long Covid. We recommend that any information you deem relevant is discussed with your NHS GP as soon as possible. It is important that you seek personalised medical advice from the GP who is in charge of your care and who knows you well.

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