Irritable bowel syndrome (IBS) is a digestive disorder that combines symptoms such as abdominal pain, bloating, constipation, diarrhea, and changes in bowel movements. It is classified as a functional gastrointestinal disorder, meaning symptoms arise from problems in how the brain and gut work together, rather than from structural damage to the gastrointestinal (GI) tract.

There is no single test to confirm IBS. Primary care providers or gastroenterologists diagnose the condition based on symptoms, medical and family history, and a physical examination. In some cases, additional tests may be recommended to rule out other conditions with similar symptoms.

Diagnostic Criteria

Healthcare providers often use established guidelines, such as the Rome 4 criteria, to diagnose IBS. An IBS diagnosis can be made if at least two of the following occur:

  • abdominal pain during bowel movements

  • pain and changes in how often bowel movements occur

  • pain and changes in stool appearance, ranging from watery to small and hard

These symptoms must be chronic, occurring at least three days per month for a minimum of three months.

Providers will usually ask detailed questions about your symptoms, so preparing a record of their frequency and severity can be helpful.

Medical History

To confirm an IBS diagnosis or rule out other possibilities, providers will review your personal and family medical history. They may ask about:

  • family health – history of inflammatory bowel disease (IBD), celiac disease, colon cancer, or other digestive conditions

  • medications – prescription or over-the-counter drugs that could cause digestive side effects

  • infections – recent viral or bacterial infections, such as gastroenteritis

  • stress – any major life events or stressors coinciding with symptom onset

  • diet – common foods eaten, eating patterns, and potential triggers

  • associated conditions – such as chronic pain, fibromyalgia, gastroesophageal reflux disease (GERD), indigestion, anxiety, depression, or somatic symptom disorder

Physical Exam

A physical examination helps identify signs of other diseases that may mimic IBS. This may include:

  • palpating the abdomen to check for bloating, swelling, or tenderness

  • listening with a stethoscope for bowel sounds

  • tapping the abdomen to identify areas of pain

  • digital rectal exam to detect growths or abnormalities

Screening for Related Conditions

In most cases, IBS can be diagnosed without further testing. However, additional tests may be ordered if symptoms suggest another condition, such as gastrointestinal infections, cancer, IBD, celiac disease, bowel obstruction, or medication side effects.

Testing is more likely if you experience:

  • unexplained weight loss (10% or more within three months)

  • fever with bowel symptoms

  • blood in the stool or black, tarry stools

  • symptoms that disrupt sleep

  • onset of IBS symptoms after age 50

  • family history of colorectal cancer, IBD, or celiac disease

Blood and Stool Tests

Blood and stool tests can help detect diseases such as Crohn’s disease, ulcerative colitis, celiac disease, anemia, and infections.

  • blood tests may include a complete blood count (CBC), C-reactive protein (inflammation marker), or celiac disease antibody testing

  • stool tests check for parasites like giardia or harmful bacteria such as C. diff

Colonoscopy

A colonoscopy allows providers to examine the inside of the large intestine using a flexible tube with a camera. During the procedure, they may look for inflammation, growths such as polyps, or other abnormalities. Biopsies can be taken for further evaluation. This test is often recommended for patients with high-risk symptoms or a family history of colon cancer or IBD.

Upper Gastrointestinal Endoscopy

An upper GI endoscopy may be performed to investigate the esophagus, stomach, and small intestine, especially if celiac disease or other upper GI issues are suspected. An endoscope is passed through the mouth, and tissue samples may be collected for biopsy. Sedation and throat numbing medication are typically used to make the procedure more comfortable.

A Quick Review

IBS is diagnosed primarily through symptom assessment, medical history, and a physical exam. While there is no definitive test, healthcare providers may use blood tests, stool tests, colonoscopy, or upper GI endoscopy to rule out other conditions. This thorough evaluation helps ensure that IBS is accurately diagnosed and