A doctor putting blood in a vile.
Some tests used to diagnose IBS include blood tests and stool sampling.

How to Test for IBS

Irritable bowel syndrome, often referred to simply as IBS, is a common and uncomfortable disorder that affects the large intestine. Estimates suggest that about 10% to 15% of the adult population worldwide suffers from some type of IBS. In this article, we will go over how to test for IBS and what the diagnosis process is like.

IBS is categorized based on the type of abnormal bowel movements an individual experiences:

  • IBS with diarrhea (IBS-D) — the majority of bowel movements are loose and watery.
  • IBS with constipation (IBS-C) — the majority of bowel movements are lumpy and hard.
  • IBS with mixed bowel movements (IBS-M) — both loose, watery and lumpy and hard bowel movements on the same day.

What Causes IBS?

The underlying cause of IBS remains unknown, but various factors have been found to be associated with the condition, including:

  • Signals between the brain and intestines may be poorly coordinated resulting in your body overreacting to normal changes that occur during digestion, leading to symptoms such as pain, constipation, or diarrhea.
  • Stronger and longer-lasting muscle contractions in the intestines can speed up the passage of food and cause bloating, gas and diarrhea. While weaker muscle contractions in the intestines can slow the passage of food and lead to symptoms of hard and dry stools.
  • IBS may develop after a severe bacterial or viral infection in the gastrointestinal system, and it may also be associated with an overgrowth of bacteria in the intestines.
  • Stress, especially during childhood, has been associated with increased IBS symptoms.
  • Bacteria, viruses and fungi normally live in the intestine; individuals with IBS have been shown to have different gut microbe composition compared to healthy individuals.

Common Symptoms of IBS

Signs and symptoms of IBS vary among patients, but most commonly include:

  • Abdominal cramping, pain and/or bloating.
  • Changes in the appearance of stool.
  • Changes in bowel habits.
  • Diarrhea, constipation, or alternating between the two.

Other symptoms may include:

  • Increased gas.
  • Mucus in the stool.

Individuals with IBS tend to have more symptoms if they eat certain foods or drink certain drinks. The most common triggers include dairy products, wheat, citrus fruits, cabbage, beans and carbonated drinks. Additionally, individuals with IBS tend to have worsening symptoms during times of increased stress.

Tests Used to Diagnose IBS

If you are suffering with GI symptoms, it is important to speak with your doctor. While there is no definitive test to diagnose IBS, in general, if a physician understands the clinical presentation of IBS, unnecessary testing can be avoided. Typically, IBS can be diagnosed when a physician recognizes specific symptom details, performs a thorough physical exam and undertakes limited diagnostic testing.

The Rome Criteria

This is often used to diagnose IBS. For this criteria to be used, a person must experience abdominal discomfort and pain that lasts on average at least one day a week for at least three months that is associated with at least two of the following:

  • Discomfort and pain related to defecation.
  • Frequency of defecation is altered.
  • Stool consistency is altered.

Your doctor will take a detailed history of symptoms and perform a thorough physical exam. Depending on their clinical impression, additional testing may be done. It’s important to keep in mind that testing is individualized and is based on various factors including symptom features, family history and the presence of accompanying factors, such as stress. Obtaining an accurate diagnosis is essential for effective treatment, and for improving your quality of life.

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Other Diagnostic Tests

The following tests may be ordered if you are suffering with IBS symptoms:

  • Blood tests — complete blood count (CBC) to evaluate for anemia, tissue damage and/or inflammation.
  • Stool sampling — examination of the stool to evaluate for blood in the stool, bacterial infection, or intestinal parasite.

Depending on the specific needs of an individual, especially for those with atypical symptoms or “red flags,” various other tests may be ordered including:

  • Anorectal manometry to measure muscle and nerve function in the anus and rectum.
  • Capsule endoscopy to detect Crohn’s disease.
  • Colonic transit to measure the movement rate of contents in the colon.
  • Blood biomarker profile to differentiate IBS from other medical conditions.
  • Hydrogen breath test to detect lactase deficiency.
  • Lactulose/glucose breath tests to detect bacteria overgrowth syndrome.

Sigmoidoscopy and Colonoscopy

Two of the most common tests that are recommended for individuals with GI symptoms that accompany red flags including rectal bleeding and/or unintentional weight loss, as well as for routine screening after the age of 50 are flexible sigmoidoscopy and/or colonoscopy. Both of these tests allow for a detailed examination of your colon. Sigmoidoscopy examines the lower half of the colon while a colonoscopy examines the whole colon:

  • Sigmoidoscopy — your doctor inserts a thin, flexible instrument, called a sigmoidoscopy, into the rectum. The sigmoidoscope is then advanced to the colon to view the lining of the rectum and lower half of the colon.
  • Colonoscopy — your doctor inserts a colonoscope through the rectum. The colonoscope is then advanced through the entire colon. During the procedure small tissue samples may be removed for biopsy, and polyps may be identified and removed, if necessary.
  • Barium enema — allows for x-ray examination of the large bowel after it is coated with barium. This test has been replaced in most cases by colonoscopy.
  • Psychological testing — questionnaires to evaluate for depression, anxiety and other mental health issues may sometimes be used as a supplement for evaluation of IBS symptoms.

Ruling Out IBS From Other Gastrointestinal Issues

As previously mentioned, when “red flags” are found, additional testing may be necessary to rule out other gastrointestinal conditions before symptoms can be attributed to IBS. These “red flags” include:

  • Blood in the stool.
  • Symptom onset after the age of 50.
  • Fever.
  • Unintentional weight loss.
  • Night-time waking due to symptoms.
  • Change in the quality of symptoms (i.e. new symptoms or different type of pain).
  • Family history of GI disease such as celiac disease, colon cancer, etc.
  • Abnormal blood tests, including anemia.
  • Recent use of antibiotics.


Irritable bowel syndrome can cause uncomfortable, and sometimes embarrassing, symptoms that can negatively impact your life. While there is no definitive test for IBS, there are various diagnostic tests available to use in conjunction with your physicians clinical impression to determine the underlying cause of your symptoms in order to develop an effective treatment plan to manage your symptoms and improve your quality of life.