Doctors do not recommend routine colonoscopy to diagnose people with irritable bowel syndrome (IBS). However, they may refer individuals to rule out other conditions, such as inflammatory bowel disease (IBD).

IBS is a functional gastrointestinal disorder that can cause changes in bowel movements, such as diarrhea, constipation, or both. Someone with IBS needs to discuss the risks of having a colonoscopy and the alternatives that may be available.

This article looks at whether people with IBS should have a colonoscopy and if it can worsen IBS. It also explores how to prepare for a colonoscopy and any possible risks.

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No, generally, doctors do not refer people with IBS for a colonoscopy unless someone presents with symptoms that doctors consider concerning signs.

Possible concerning signs may include:

The American College of Gastroenterology does not usually recommend routine colonoscopy in those under 45 with IBS symptoms and no warning signs or features.

People with no alarming signs may receive a diagnosis through blood and stool tests. Specialized tests can accurately determine whether a person has IBS with diarrhea or IBD by looking for specific molecules in the blood.

However, doctors would refer people with symptoms consistent with IBS and warning signs for a colonoscopy. This will help rule out other causes, such as IBD and colorectal cancer.

Indications a doctor may refer someone for a colonoscopy may include:

Sometimes, doctors may perform a biopsy during colonoscopy in people with diarrhea to confirm the other possible diagnoses. Biopsy involves taking a small sample of the tissue.

A person can discuss possible options with their doctor, who can determine the best method to diagnose them.

The preparation for a colonoscopy is generally the same for someone with IBS as it is for a person without the condition also undergoing the procedure. Still, some doctors might advise people with IBS-C or constipation to undergo more extensive preparations.

An adequate level of bowel cleansing is important for a successful colonoscopy. Usually, a doctor will provide specific instructions on how to prepare for the procedure.

Bowel preparation

This involves taking a laxative medication to clean out the bowel. This may be in pill, liquid, or powder form. Some people will drink the liquid over a scheduled time, usually the night before and the morning of the procedure.

Doctors may also recommend enemas. The prep will cause diarrhea, so a person might want to be close to a toilet.

Dietary changes

People need to avoid foods that are high in fiber several days before the procedure, such as:

  • whole grains
  • raw vegetables
  • beans
  • nuts and seeds

They must also drink clear liquids for at least 1 day before the procedure. This may include only drinking:

  • tea or coffee with no milk
  • fruit juice with no pulp
  • water

Read more about how to prepare for a colonoscopy.

There is limited research on whether a colonoscopy worsens IBS, and an individual’s experiences may also vary.

Anecdotally, people report that the following may cause IBS to worsen:

  • bowel preparation for a colonoscopy
  • the actual process of a doctor inserting and moving the colonoscope itself
  • any biopsies taken

Bowel preparation can sometimes cause excessive bloating and gas, which might worsen the pain and discomfort relating to IBS.

While very little research focuses on the effects of the procedure on IBS, researchers have examined the risks of it worsening IBD.

Additional 2019 research suggests that the colonoscopy procedure, or bowel preparation, may exacerbate IBD symptoms.

Besides those above, the risks relating to a colonoscopy are likely to be similar whether someone has IBS or not.

Potential risks of a colonoscopy include:

  • bleeding
  • perforation, leading to a hole in the colon
  • a reaction to the sedative during the procedure
  • severe pain in the abdomen
  • tears
  • infection

In 3 out of every 10,000 procedures, perforation may occur, and in 15 out of every 10,000 procedures, bleeding occurs. Most cases occur in people who are older or who have undergone polyps removal.

Experts do not recommend routine colonoscopy in people under 45, with IBS symptoms and no alarming signs or features. Individuals may have blood and stool tests to help diagnose their condition.

However, doctors refer people for a colonoscopy if they have symptoms consistent with IBS and warning signs. This will help rule out other causes, such as IBD and cancer.

There is insufficient evidence to determine whether a colonoscopy makes IBS worse.

People need to follow the doctor’s instructions to prepare for a colonoscopy.