There’s no single test for irritable bowel syndrome (IBS). Instead, doctors diagnose IBS based on your symptoms and may use additional tests to rule out other causes.

What Criteria Do Doctors Use To Diagnose IBS?

Doctors often rely on established diagnostic standards, such as the Rome 4 criteria, to diagnose IBS.

An IBS diagnosis can be made if you have at least two of the following:

• Abdominal pain when you make a bowel movement
• Pain and changes in how often you make a bowel movement
• Pain and changes in how your poop looks, which can range from watery to hard and small

These symptoms must also occur repeatedly and be ongoing, or at least three days a month for three months.

Tip: Doctors will typically ask many questions about your symptoms. Go to the appointment prepared. Keep track of your symptoms and their frequency.

Reviewing Your Medical History

To help confirm an IBS diagnosis or rule out other possible causes, a doctor must understand your medical history.

To take your medical history, a doctor will ask about:

Associated conditions: They may ask about your history of IBS-related diseases. Examples include fibromyalgia, gastroesophageal reflux disease (GERD), indigestion, anxiety, and depression.

Diet: Your diet plays a key role in digestive diseases. A doctor will want to know about the foods you eat and your typical eating habits.

Family health: They will likely ask if you have any relatives with a history of inflammatory bowel disease (IBD), celiac disease, colon cancer, or other digestive diseases.

Infections: They may ask if you have had any recent infections, such as gastroenteritis (infection of the intestines).

Medications: Certain medications can cause digestive symptoms. They may discuss any prescription and over-the-counter (OTC) drugs you are taking.
Stress: They may ask if you have had stress when your symptoms began.

What To Expect During a Physical Exam

During a physical exam, a doctor will look for signs of diseases that could cause IBS symptoms.

A physical exam may involve:

• Listening with a stethoscope to the sounds your abdomen makes
• Palpating (feeling) your abdomen for signs of bloating or swelling
• Performing a digital rectal exam, in which a doctor feels inside your anus with a gloved finger for signs of growths
• Tapping on your abdomen to find areas of pain or tenderness

Ruling Out Conditions That Can Mimic IBS

Doctors can usually diagnose IBS without further testing.

However, you may need additional tests to rule out other potential causes of your symptoms, such as:

• Bowel obstruction
• Cancer
• Celiac disease
• Gastrointestinal infections
• IBD
• Lactose intolerance
• Medication side effect

Blood Tests

For a blood test, a doctor collects a blood sample from your vein and sends it to a lab.

Examples of blood tests include:

• A complete blood count (CBC)
• C-reactive protein, which is a sign of inflammation
• Serology testing, which measures antibodies in your blood that are a sign of celiac disease

Stool Tests

For a stool test, a doctor will give you a kit to collect your poop and send it to a lab. The lab will test your stool for signs of parasites like Giardia or bacteria like Clostridioides difficile.

Colonoscopy

A colonoscopy is a procedure that allows doctors to see the inside of the large intestine. They will insert a flexible tube with a camera into your rectum and colon.

During a colonoscopy, a doctor looks for polyps (non-cancerous growths) and inflammation. They may also perform a biopsy and take a small tissue sample for testing.

Note: Colonoscopies and endoscopies are not required to make an IBS diagnosis and should be used on a situational-only basis, depending on whether you have concerning symptoms.

Upper Gastrointestinal Endoscopy

An upper endoscopy views the upper part of your digestive tract. It can check the inside of your esophagus, stomach, and small intestine.

During an upper endoscopy, a doctor passes an endoscope through your mouth to your esophagus and stomach. This tool sends images of the tissues to a screen. A doctor may collect a tissue sample for biopsy.

Note: You will receive medications to help with pain and relaxation and to numb your throat.

Hydrogen Breath Test

A doctor may administer a hydrogen breath test to rule out lactose intolerance (but not to diagnose IBS). People with lactose intolerance cannot digest lactose, a sugar found in dairy products.

During a hydrogen breath test, you will breathe out into a container before and after drinking a lactose-rich beverage. High levels of hydrogen in your breath are a sign of lactose intolerance.

When Should You See a Doctor Right Away?

Seek medical attention right away if you have concerning symptoms, such as:

• Bloody or tar-like stools
• Family history of colorectal cancer, IBD, or celiac disease
• Fever
• IBS symptoms that start after age 45
• Symptoms that disrupt sleep
• Unintended weight loss (i.e., losing at least 10% of your body weight within three months)