Acute severe ulcerative colitis (ASUC) is a potentially life threatening complication of ulcerative colitis. Doctors typically treat the condition in the hospital with medication, but some people may require surgery.

ASUC affects roughly 20% of people with ulcerative colitis, which is a type of chronic inflammatory bowel disease (IBD) that primarily affects a person’s colon and rectum.

During the last few decades, ulcerative colitis has become widespread in Western societies affecting 1 in 200 people. However, incidence rates are also rising globally.

This article examines ASUC in more detail, discussing its symptoms, causes, and how doctors treat it. In addition, the article explores the potential outlook for people with ASUC.

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When diagnosing ASUC, doctors use a set of criteria based on symptoms and tests. The criteria include passing bloody stools at least 6 times a day alongside at least one of the following signs of systemic toxicity:

Researchers suggest that despite these criteria being 60 years old, they remain the most sensitive way to define ASUC. However, sometimes, doctors may use other criteria to help diagnose ASUC.

People with ASUC are likely to experience some of the symptoms of ulcerative colitis.

Symptoms of ulcerative colitis

Common symptoms of ulcerative colitis include:

Symptoms that may appear with more severe ulcerative colitis include:

People with ulcerative colitis should speak with a healthcare professional as soon as possible if they notice any new or worsening symptoms.

Learn more about IBD diagnosis here.

ASUC occurs as a result of someone having ulcerative colitis. Experts estimate that 20–25% of people with ulcerative colitis may experience a severe exacerbation (flare) requiring hospitalization.

Researchers are not sure exactly what causes ulcerative colitis, but some suggest that the following factors may play a role:

  • genes
  • abnormal immune reactions leading to inflammation
  • the gut microbiome, people with IBD may have different gut microbiomes than those who do not have the condition
  • environmental factors outside the body that interact with someone’s genes, gut microbiome, and immune system

Learn more about managing an ulcerative colitis flare here.

The authors of a recent review explain that doctors require more high quality evidence to help them inform their management and treatment approach for ASUC.

Healthcare professionals may treat and manage the condition by:

  • recognizing individuals at risk of ASUC early
  • hospitalizing the individual, providing fluid replacement, assessing and optimizing their nutrition status, and taking steps to prevent the risk of deep vein thrombosis
  • assessing the individual using stool tests, blood tests, imaging tests, and biopsies
  • initial treatment, including treating infections and using intravenous corticosteroids
  • reassessment on day three with further treatment of corticosteroids and immunosuppressant medications or referral for colectomy

Experts explain that about a third of individuals will not respond to intravenous corticosteroids. People who do not respond to steroid therapy between days 3 and 5 of experiencing ASUC are at a high risk of corticosteroid therapy failure. In this case, doctors may initiate ‘rescue’ therapy or surgery.

Rescue therapy consists of treating someone with medications such as infliximab or cyclosporine. If a person does not respond to these medications, they may need a colectomy.


Some people with ASUC may need a colectomy, which is a surgical procedure to remove all or part of the colon.

Doctors may recommend an urgent colectomy in people who have severe internal bleeding, intestinal perforation, toxic dilation (swelling and inflammation in the deeper layers of the colon), or who are not responding to medications.

Undergoing a colectomy within 7 days of not responding to intensive steroid treatment may improve surgical outcomes and lower the risk of death.

However, colectomy has risks, including infection and sepsis, but research suggests the risk may be less severe than continuing medication therapy in people who are severely ill.

People with ASUC should speak with a healthcare professional about what to expect before, during, and after colectomy, including the benefits and risks of the procedure.

Learn more about colectomy here.

A 2021 review explains that colectomy rates for ASUC have decreased but remain high, at around 30%.

Treatments for ASUC, such as immunosuppressant medications, reduce remission rates in the short term. However, 50% of people who initially respond to cyclosporine will still require a colectomy in the long term. Similarly, about 20% of those who respond to infliximab will require a colectomy in the long term.

Additionally, medications have helped to decrease the mortality rate for ASUC.

A person with ASUC should speak with a doctor about their individual outlook.

ASUC occurs in people with ulcerative colitis who have a severe flare. The diagnostic criteria for ASUC include passing bloody stools at least 6 times a day alongside at least one sign of systemic toxicity.

Doctors typically treat ASUC with corticosteroids and immunosuppressant medications. However, individuals who do not respond to medications or have life threatening symptoms may require a colectomy.

People should contact a doctor as soon as possible if they experience any new or worsening symptoms of ulcerative colitis or suspect they are experiencing ASUC.