Diagnosing IBS

The first step in making diagnosing IBS is for the healthcare provider to identify if an individual has symptoms of IBS. 

This includes abdominal pain at least 1 day a week in the last 3 months, associated with two or more of the following:

  • The abdominal pain is associated with a bowel movement, or
  • a change in how their bowel movements look, or
  • a change in how often they have bowl movements.

When a person has typical IBS symptoms, non-worrying findings on physical examination and normal blood and stool tests, studies show they can be confidently diagnosed with IBS.

The next important step is to look for signs and symptoms that raise concerns for a condition other than IBS, such as inflammatory bowel disease (IBD) (ulcerative colitis and Crohn’s disease) or celiac disease. These signs and symptoms have been referred to as “alarm signs” or “red flags.”

They include:

  • Blood in bowel movements – This blood can be bright red to black in color and may be in or around bowel movements.
  • Low blood counts (anemia) – This is determined by blood work or lab tests ordered by a healthcare provider.
  • New onset of symptoms over the age of 50.
  • Losing weight without trying.
  • Diarrhea that wakes you up from sleep at night.
  • A family history of IBD, colon cancer, or celiac disease.

These alarm signs are usually not explained by IBS and can represent other medical problems. When these symptoms and signs occur, they should be brought immediately to the attention of a healthcare provider who may perform additional tests.

Digital Rectal Examination (DRE)

A digital rectal exam (DRE) is an examination of the lower rectum and anus. The healthcare provider uses a gloved, lubricated finger in the anus to check for any abnormal findings. The provider will first look at the outside of the anus for hemorrhoids or fissures.

The DRE is also done to evaluate the functioning of the anal and pelvic floor muscles, particularly if there is incontinence (involuntary passage of stool) or severe constipation with a feeling of incomplete emptying after a bowel movement.

Colon Examination

A colon examination, such as a colonoscopy, should be performed in all patients at or above the age of 45 who have not had one previously, as a screening test for colon polyps and cancer and not specifically for IBS. However, they may be done for younger patients particularly if the healthcare provider is suspicious of other bowel diseases such as ulcerative colitis or Crohn’s disease.

For those with mostly diarrhea, biopsies (small tissue samplings) can be taken during the procedure to determine if microscopic colitis or mild inflammation of the colon is present.

Blood Testing for Celiac Disease

Celiac disease is a genetic condition of the small intestine that develops in people intolerant to gluten (a common ingredient in many foods including grains, wheat, rye and barely, as well as many processed foods). It causes malabsorption of nutrients and food and results in symptoms similar to those in IBS. If the blood test is positive, an upper endoscopy should be performed to examine and biopsy the small intestine to confirm the diagnosis.

Stool Tests

In patients with diarrhea symptoms, fecal calprotectin or lactoferrin and a stool test for a parasite called Giardia are recommended to exclude inflammatory and infectious causes of chronic diarrhea.

Importantly, even if another diagnosis is made, it may exist along with a diagnosis of IBS. The healthcare provider will then need to decide which condition or conditions are to be treated and how.

Learn more about testing in IBS.

Adapted from IFFGD Publication #101 IBS Brochure by By: Lin Chang MD, Professor of Medicine at the David Geffen School of Medicine at UCLA, Los Angeles, CA; adapted from article by Douglas A. Drossman MD, Drossman Gastroenterology PLLC, Chapel Hill, NC; edited by William D. Chey MD, Nostrant Collegiate Professor, University of Michigan, Ann Arbor, MI

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IFFGD is a nonprofit education and research organization. Our mission is to inform, assist, and support people affected by gastrointestinal disorders.

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