What is IBD?

IBD stands for Inflammatory bowel disease, a term that covers two conditions that cause chronic inflammation in the GI (gastrointestinal tract):

  • Crohn’s disease;
  • Ulcerative colitis.

People with IBD have a higher risk of developing blood clots, which are clumps of blood that block the blood flow in the arteries or veins. Blood clots can damage the organs they reach, such as the heart or the brain, and cause serious complications like heart attacks and strokes.

The exact reason why IBD increases the risk of blood clots is not known, but it is very important that patients are aware of this risk and take steps to prevent it.

Causes and risk factors for blood clots

Blood clots can be caused by many factors, such as:

  • Atherosclerosis: a condition where plaque builds up in the arteries and narrows them;
  • Atrial fibrillation: an irregular heartbeat that can cause blood to pool in the heart chambers and form clots;
  • Diabetes: a disease that affects how the body uses sugar and can damage the blood vessels;
  • DVT (deep vein thrombosis): a blood clot that forms in a deep vein, usually in the leg;
  • Heart failure: a condition where the heart cannot pump enough blood to meet the body’s needs;
  • Metabolic syndrome: a cluster of risk factors that increase the chance of heart disease, diabetes, and stroke;
  • Peripheral artery disease: a condition where the arteries that supply blood to the limbs are narrowed or blocked;
  • Vasculitis: an inflammation of the blood vessels.

Some of the risk factors that make blood clots more likely are:

  • Cancer: a disease that causes abnormal cells to grow and divide uncontrollably;
  • Dehydration: a condition where the body loses more water than it takes in;
  • Genetics: inherited traits that affect how the blood clots;
  • Hospitalization: being confined to a bed or having surgery can reduce blood flow and increase clotting;
  • Injury to a vein: trauma or damage to a vein can trigger clotting;
  • Obesity and overweight: having excess body weight can put pressure on the veins and affect blood flow;
  • Personal history of blood clots: having had a blood clot before increases the chance of having another one;
  • Personal history of miscarriages: having had one or more miscarriages may indicate a clotting disorder;
  • Recent accident (such as a car accident): an accident can cause injuries or shock that can affect blood clotting;
  • Sitting for long periods or being on bed rest: staying still for too long can slow down blood flow and promote clotting;
  • Smoking: tobacco use can damage the blood vessels and make the blood stickier;
  • Surgery: having an operation can expose the blood to foreign substances or damage the blood vessels, which can trigger clotting;
  • Use of estrogen-based medications, such as birth control or hormone therapy: these medications can affect how the blood clots and increase the risk of DVT or pulmonary embolism.

Research on the link between blood clots and IBD

Several studies have shown that people with IBD have a higher risk of developing blood clots than people without IBD. For example:

  • A Danish study that followed people with IBD from 1980 to 2007 found that they had twice the risk of pulmonary embolism (a blood clot in the lungs) and DVT than people without IBD. This increased risk remained even after adjusting for other potential risk factors, such as age, sex, comorbidities, or medication use.
  • A British study that compared people with IBD who had active disease (flare-ups) or inactive disease (remission) with people without IBD found that both groups of IBD patients had a much higher risk of developing blood clots than the control group. The risk was especially high for hospitalized IBD patients, who had eight times the risk of developing blood clots than hospitalized non-IBD patients.

However, not all people with IBD have the same risk of developing blood clots. The personal risk depends on many factors, such as:

  • Age: older people have a higher risk of developing blood clots than younger people;
  • Family history: having relatives who had blood clots increases the risk of having them too;
  • Activity level: being physically active can improve blood circulation and prevent clotting;
  • Medications: some medications can affect how the blood clots, either increasing or decreasing the risk;
  • Pregnancy: being pregnant can change how the blood clots and increase the risk of DVT or pulmonary embolism.

According to the Guidelines from the Canadian Association of Gastroenterology published in 2014, it is only recommended to use anticoagulant medications (medications that prevent blood clotting) for patients with IBD after surgery or while hospitalized, and not to prevent blood clots on a daily basis.


The best way to prevent blood clots is to address the underlying causes and risk factors. Some of the general recommendations are to:

  • Exercise: physical activity can improve blood flow and reduce inflammation;
  • Keep a healthy weight: losing excess weight can relieve pressure on the veins and improve blood circulation;
  • Drink enough water: staying hydrated can prevent dehydration and keep the blood from becoming too thick;
  • Manage related conditions (i.e. diabetes): controlling blood sugar levels and other health problems can reduce the damage to the blood vessels and the risk of clotting.

It is also very important that people with IBD work with their doctors to find the best medication to prevent blood clots. Anti-clotting medications might be prescribed, but only after surgery or while hospitalized, and under close monitoring.


Blood clots are a serious complication that can affect people with IBD. It is essential that patients are aware of this risk and take steps to prevent it. If you suffer from IBD and have concerns about your personal risk, you should talk to your doctor and other specialists, such as a gastroenterologist.

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