This Medical Monday series is about risk factors for venous thromboembolism, VTE (pulmonary embolism and DVT). The post ‘Are you on the red or blue team?‘ outlines the difference between arterial and venous clots.
We are going to cover
Strong risk factors; being in hospital, having surgery and immobility
Moderate risk factors; age (60+), a previous blood clot, family history of blood clots, thrombophilia, cancer, contraceptive pill and hormone replacement therapy
Other risk factors; obesity, pregnancy, smoking and alcohol
Having a previous blood clot
If you have already had a blood clot, your risk of a second clot is significantly increased compared to somebody who has never had a clot. Even if your first clot was due to an obvious cause like a broken leg or major surgery your risk is still higher than normal. It is quoted that approximately 1% of people who had a DVT or PE related to surgery will have a second clot within 12 months. The risk is about 3% per year after a clot related to flying and about 4.5% for clots due to other risk factors. The risk is highest in somebody who had a first clot for no apparent reason (an idiopathic clot); in this group about 15% will have a second clot within 12 months.
At one time it was thought that the risk diminished over time, but it is now clear from some large studies that the risk of another blood clot is cumulative, this means the risk is still present many years after an event. For example after a blood clot that occurred spontaneously with no identified risk factor, the risk of a second clot is 15% at 1 years, 26% at 3 years, 40% at 5 years and over 50% at 10 years. So if you have a blood clot today “out of the blue”, you have a 50% chance of having another one within 10 years. Also if your first clot was a pulmonary embolus there is a high chance that your second clot will also be a pulmonary embolus.
Venous thrombosis is a chronic disease
These large population studies have helped us to better understand the nature of venous thrombosis. It is now clear that if you have had more than one blood clot you have a chronic condition with an ongoing risk of further clots. As a result many people with a history of recurrent clots are now remaining on long-term anticoagulant therapy.
In fact it is now becoming clear that venous thromboembolic disease is a chronic condition for many people
If you have had several blood clots you should be looking at staying on long-term anticoagulants. This can be a difficult decision as it is a big committment to take medication for the rest of your life, but blood clots are potentially life-threatening. It is important to weigh up the pros and cons of anticoagulant therapy, this is something you should discuss carefully with your doctor; sometimes the risk of bleeding may outweigh the benefits of staying on treatment. For some people less intensive treatment such as aspirin may be a good option.