Clotting (VTE) Risk in IBD

People with inflammatory bowel disease (IBD) have a higher-than-average risk of blood clots in the veins, called venous thromboembolism (VTE). This includes clots in the legs and lungs that can be life threatening but are often preventable. Risk peaks during flares, hospital stays, and after surgery, so hospitals use blood thinners and other strategies to lower this risk and protect patients.

Key Takeaways

• IBD roughly doubles or triples the risk of venous blood clots compared with people without IBD, in both Crohn’s disease and ulcerative colitis. (pubmed.ncbi.nlm.nih.gov)

• Risk is highest during flares, hospitalization, and after surgery, and is also higher with steroids, older age, prior clots, and other medical problems. (pubmed.ncbi.nlm.nih.gov)

• Guidelines recommend preventive blood thinners for almost all hospitalized IBD patients, unless there is active major bleeding or another strong reason not to use them. (pmc.ncbi.nlm.nih.gov)

• Preventive treatment in hospital clearly lowers clot risk and does not appear to increase serious bleeding in IBD. (pubmed.ncbi.nlm.nih.gov)

• Awareness of clot symptoms like one-sided leg swelling or sudden chest pain can prompt faster emergency care.

• Good control of bowel inflammation and limiting steroid use are long-term strategies that may help lower clot risk over time. (pubmed.ncbi.nlm.nih.gov)

What is VTE and how is it linked to IBD?

Venous thromboembolism (VTE) means a blood clot forming in a vein. The two main types are:

• Deep vein thrombosis (DVT) – usually a clot in a deep leg vein.

• Pulmonary embolism (PE) – a clot that travels to the lungs.

Large studies and meta-analyses show that people with IBD have about a 2‑ to 3‑fold higher risk of VTE compared with people without IBD. (pubmed.ncbi.nlm.nih.gov) This increased risk is seen in both Crohn’s disease and ulcerative colitis, and in adults and children. (pubmed.ncbi.nlm.nih.gov)

Because VTE can cause serious illness or death, it is now recognized as an important extraintestinal manifestation of IBD.

Why IBD increases clot risk

IBD is not only inflammation in the gut. It is a systemic inflammatory condition. That inflammation activates clotting pathways, makes platelets “stickier,” and alters the normal balance between clot formation and clot breakdown. (pubmed.ncbi.nlm.nih.gov)

Several factors raise VTE risk in IBD:

• Active disease and flares – Clot risk is much higher when disease is active, even outside the hospital. (pubmed.ncbi.nlm.nih.gov)

• Hospitalization and surgery – Being in bed, having surgery, anesthesia, and central lines all add to risk. (jamanetwork.com)

• Steroid treatment – Systemic corticosteroids are linked to higher VTE risk. (pubmed.ncbi.nlm.nih.gov)

• Older age, obesity, smoking, serious comorbidities, or prior clots – These common medical risk factors further increase the chance of VTE. (pmc.ncbi.nlm.nih.gov)

• Some medications – Certain Janus kinase (JAK) inhibitors carry specific clot warnings, especially in people who already have other VTE risks. (pubmed.ncbi.nlm.nih.gov)

The risk does not end at hospital discharge. Studies show an elevated VTE rate for several weeks to months after an IBD hospitalization, especially in higher risk groups. (pubmed.ncbi.nlm.nih.gov)

How hospitals prevent clots in IBD

Pharmacologic prevention (blood thinners)

Most guidelines now state that all hospitalized patients with IBD should receive pharmacologic thromboprophylaxis, unless there is active major bleeding or another strong contraindication. (pmc.ncbi.nlm.nih.gov)

Common medicines include:

• Low molecular weight heparin (LMWH) injections once or twice daily.

• Occasionally fondaparinux or low-dose unfractionated heparin, depending on kidney function and local practice. (pmc.ncbi.nlm.nih.gov)

Key points from large observational studies:

• Preventive heparin use in hospitalized IBD patients lowers the rate of VTE compared with no prophylaxis. (pubmed.ncbi.nlm.nih.gov)

• These studies did not find an increase in major bleeding, even in many patients with rectal bleeding from colitis. (pubmed.ncbi.nlm.nih.gov)

Because rectal bleeding is common in moderate to severe ulcerative colitis, clinicians often balance the visible bleeding against the very real risk of a life‑threatening PE. Current consensus suggests that prophylactic doses of heparin are usually safe, and that mild to moderate rectal bleeding alone is not a reason to omit prophylaxis. (pmc.ncbi.nlm.nih.gov)

In children and adolescents with IBD, VTE risk is also increased, especially during hospitalization, although evidence on the safest and most effective dosing is more limited. (pubmed.ncbi.nlm.nih.gov) Many pediatric centers use risk scores and local protocols to decide when to use blood thinners.

Mechanical prevention and mobility

Hospitals also use mechanical methods to keep blood moving in the legs, especially when a person cannot walk much:

• Intermittent pneumatic compression devices – inflatable sleeves around the legs that rhythmically squeeze the calves. (aafp.org)

• Graduated compression stockings, usually as an add‑on in some surgical or very high‑risk settings.

These methods are often combined with blood thinners. Early and frequent walking, sitting up, and good hydration are also simple but important parts of prevention.

After leaving the hospital

Research shows that VTE risk can stay elevated for several weeks after IBD hospitalization, especially after major surgery or in people with prior clots or many comorbidities. (pubmed.ncbi.nlm.nih.gov)

International consensus guidance suggests:

• Routine extended prophylaxis after discharge is not recommended for everyone with IBD.

• Extended blood thinner use may be considered in selected very high‑risk patients, such as those with a recent VTE, cancer, or marked immobility, but this decision is individualized. (pmc.ncbi.nlm.nih.gov)

Recognizing possible clot symptoms

Caregivers and patients should know the main warning signs of VTE so they can seek urgent help:

Possible DVT (usually in one leg):

• New swelling, often below the knee

• Pain or tenderness, especially in the calf

• Warmth or skin color change on the affected side

Possible PE:

• Sudden shortness of breath not explained by usual IBD symptoms

• Sharp chest pain that worsens with deep breaths

• Rapid heart rate, feeling faint, or coughing up blood

Any of these symptoms, especially in someone recently hospitalized, after surgery, or in a severe flare, should trigger emergency evaluation.

What patients, families, and caregivers can do

Although treatment decisions belong to the medical team, families and caregivers can help protect against VTE by:

• Supporting consistent IBD treatment to keep inflammation under control and reduce flares over the long term. (pubmed.ncbi.nlm.nih.gov)

• Asking about clot prevention plans during any hospital stay or planned surgery, including whether blood thinners and mechanical devices will be used. (pmc.ncbi.nlm.nih.gov)

• Making sure staff know about personal risk factors, such as prior VTE, strong family history of clots, known clotting disorders, cancer, hormone therapy with estrogen, smoking, or significant mobility limits. (pmc.ncbi.nlm.nih.gov)

• Encouraging safe movement in hospital, such as sitting up and walking with assistance when the care team allows it.

• Watching for red‑flag symptoms of DVT or PE during and after hospitalization and seeking urgent care if they appear.

FAQs

Is clot risk higher in Crohn’s disease or ulcerative colitis?

Most studies show increased VTE risk in both Crohn’s disease and ulcerative colitis, roughly 2 times or more compared with people without IBD. Some data suggest that risk may be slightly higher in ulcerative colitis, especially in older adults and in those with more severe disease, but both groups clearly have elevated risk. (pubmed.ncbi.nlm.nih.gov)

Do biologic medicines increase or decrease VTE risk?

Current evidence suggests that anti‑TNF biologics may actually lower thrombotic risk, likely by calming systemic inflammation. (pubmed.ncbi.nlm.nih.gov) Some newer drugs, such as certain JAK inhibitors, have VTE warnings in people who already have high baseline risk. (pubmed.ncbi.nlm.nih.gov) Decisions about these medicines weigh bowel control, infection risk, and clot risk together.

Why do doctors give blood thinners even when there is rectal bleeding?

In hospitalized IBD, rectal bleeding often comes from inflamed colon tissue rather than a large artery or vein. Studies and expert consensus indicate that prophylactic‑dose heparin does not meaningfully increase serious IBD‑related bleeding, while it significantly cuts the risk of dangerous clots. (pmc.ncbi.nlm.nih.gov) For this reason, mild to moderate rectal bleeding alone is usually not considered a reason to skip clot prevention.