Irritable bowel syndrome (IBS) doesn’t cause visible damage to the digestive tract, but it does affect how the large intestine works. Because of this, it can take some testing to find out if you have IBS. The first step is noticing your symptoms, such as belly pain, gas, constipation, or diarrhea. Keeping track of when these symptoms happen can help. Your doctor will then check for other causes of your stomach and bowel problems. Inflammatory bowel disease (IBD) is often confused with IBS. While both conditions have similar symptoms, they’re not caused by the same things. They also require different treatments. The most common types of IBD are Crohn’s disease and ulcerative colitis. Part of your IBS diagnosis will include screening for these conditions.

How Does a Doctor Diagnose You With IBS?

Usually, a gastroenterologist is the type of doctor who diagnoses IBS. There’s no single test for it. Instead, the doctor will review your medical history, symptoms, and lab work to put together the pieces of the puzzle.

Medical History

Medical history is a record of your past and current health. First, your doctor will ask detailed questions. They’ll want to know:

• What bowel symptoms you have, such as diarrhea and constipation
• How long you’ve had symptoms
• How often or when the symptoms occur

They may also ask questions about your mental health and any history of trauma. Many people with IBS also have depression, anxiety, or a past of abuse that raises their risk of IBS.

Also, your family history (the health conditions your close relatives have) can help doctors understand your risk for digestive diseases. If members of your family have had similar problems, it may point to a genetic connection. Knowing this information can give you and your doctor a clearer picture of what to watch for and how to manage your health.

Doctors may use the Rome IV criteria for diagnosing IBS. These criteria focus on how long you’ve had symptoms and what those symptoms look like.

To meet the Rome IV criteria, you need to have digestive symptoms for at least six months and abdominal (stomach) pain at least once a week over the past three months.

The stomach pain must also be linked to at least two of these factors:

• The pain changes when you go to the bathroom — It may get better or worse after a bowel movement.
• You have changes in how often you go to the bathroom — More often or less often than usual.
• You notice changes in the type of stool you have — It could be watery or loose (diarrhea), very hard (constipation), or sometimes both.

Blood and Stool Tests

Your doctor can also run lab tests on your blood and stool samples for more clues about what’s going on in your body. These tests can help rule out other conditions and check for complications.

Blood tests can show:

• High levels of inflammation — A sign of inflammatory bowel diseases, like Crohn’s disease and ulcerative colitis
• Anemia – Happens when you have low red blood cells, and in this particular case, it can be caused by gastrointestinal (GI) bleeding or other problems
• Electrolyte imbalance — Common with any condition that causes vomiting and diarrhea
• Infections — Can mimic or worsen digestive symptoms
• Kidney dysfunction — A complication of Crohn’s, ulcerative colitis, and conditions of severe diarrhea
• Abnormal nutrient levels — Related to poor absorption in the intestines

Stool culture tests check for infection and blood in the GI tract.

If your symptoms are caused by irritable bowel syndrome, your test results will come back as normal. If any tests aren’t normal, your doctor may suspect that your GI symptoms are caused by another condition.

Warning signs of another bowel disease or complication of IBS may mean you need medical attention.

These warning signs may include:

• Fever
• Rectal bleeding or blood in feces
• Diarrhea or abdominal pain that wakes you up at night
• Vomiting
• Unexplained weight loss

Imaging Scans

Imaging tests are helpful ways to take a look inside the body. These can include:

• X-rays — Use a small amount of radiation to take quick pictures of the inside of your body
• Computed tomography (CT) scans — Combine X-ray images to create detailed cross-sections of your organs
• Ultrasounds — Use sound waves to make real-time images, often used to look at soft tissues and blood flow
• Magnetic resonance imaging (MRI) — Uses magnets and radio waves to create very detailed pictures of your organs and tissues

Barium is a chemical that’s used in some imaging tests. It provides contrast, making it easier to see inside the tube-like organs of your body, like the GI tract. You may need to swallow a contrast solution or receive a barium enema. Imaging scans can detect signs of inflammatory bowel disease.

Endoscopies and Biopsy

An endoscopy is a test that’s done by putting a small camera into the body. The camera may be inserted into the stomach through the mouth (upper endoscopy) or into the colon through the rectum (sigmoidoscopy or colonoscopy).

People are usually sedated during endoscopy tests. During the examination, your doctor may use tools to remove tiny portions of affected tissue for analysis. This is called a biopsy. These procedures can be done during an outpatient appointment, with no hospitalization required.

Bowel preparation may be required before a colonoscopy or sigmoidoscopy. Bowel prep, as it is called, can involve changes to your diet starting hours or even days before the procedure. It sometimes includes taking medication to trigger diarrhea. Different doctors prefer different bowel prep regimens. The goal of bowel prep is to clear out the colon to allow a clear view during the colonoscopy.

Endoscopy and biopsy check for signs of damage in your digestive system. Since IBS doesn’t cause damage, any findings may suggest that the person has a different GI condition.

Ruling Out Other Conditions

Dozens of other conditions can produce IBS-like symptoms. These must be ruled out to confirm irritable bowel syndrome. The process of ruling out similar conditions is referred to as differential diagnosis.

Examples of conditions that can seem similar to IBS include:

• Crohn’s disease
• Ulcerative colitis
• Microscopic colitis
• Fibromyalgia
• Parasites such as Giardia
• Celiac disease
• Lactose intolerance

In addition, many medications have side effects that lead to IBS-like symptoms, especially constipation.

In some cases, it’s easy to rule out other conditions. Your doctor will just ask about your medical history or do some simple blood tests. Other times, several tests are needed. If you have IBS plus another disease at the same time, it can be tricky to sort everything out. You may end up getting diagnosed with multiple conditions.

Join the Conversation

On myIBSteam, people share their experiences with irritable bowel syndrome, get advice, and find support from others who understand.

What’s your IBS diagnosis story? Let others know in the comments below.