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There isn't a test that can tell your doctor whether you have irritable bowel syndrome (IBS). It's not a disease that will show up on a scan.

Your doctor will decide if you have IBS by asking you questions about your symptoms. He or she will examine you to make sure nothing else could be causing your symptoms. He or she may also order blood tests to rule out other illnesses.

You doctor will ask you about your symptoms and any health problems you've had in the past. He or she will also physically examine your abdomen. This is to make sure there are no swellings or lumps, and no tenderness.

Your doctor may also need to examine your rectum. He or she will want to make sure you have no swellings or lumps, and no bleeding.

There is guidance for doctors on how to diagnose IBS.^{1 2} It's mostly used to choose the right people to take part in research about treatments for IBS. Doctors don't always use these guidelines if they're not choosing people to take part in a study. But if you'd like to read more, see Guidance for diagnosing irritable bowel syndrome.

Your doctor will probably order some blood tests. These are to rule out other, more serious diseases. You may have:¹

• A full blood count. This is to check for anemia and infections. Anemia means you don't have enough oxygen-carrying red blood cells. This can happen if you've been bleeding because of another condition in your bowels, such as small growths (polyps) or cancer. An infection in your bowels can cause symptoms similar to IBS
• Blood tests to check for other, more serious problems in your bowels. These include inflammatory bowel disease and celiac disease. To read more, see Other problems in the bowels.

Your doctor may order more laboratory tests to make sure you don't have another illness. Or you might be referred to see a specialist (a gastroenterologist).

You could have:¹

• A stool test to check you don't have an infection. You'll be asked to pass a stool, which is then sent to a laboratory
• Your hormone levels checked. This is to see if your thyroid gland is working properly
• A breath test, to see if you're intolerant to a food, such as lactose. Lactose is found in dairy products like milk and cheese. Being intolerant means your body can't absorb the food properly. But only a small number of people find a reason for their symptoms.

A specialist might want to arrange tests to look at what's happening inside your bowel. You won't be asked to have these tests unless your doctor thinks your symptoms might be caused by a disease that isn't IBS. Here are the tests you might have.

• Sigmoidoscopy
• Colonoscopy
• Barium enema

Some experts think there's no point doing a lot of tests unless you have alarm signs.³ Alarm signs could mean you have a more serious illness. Your doctor will want to find out if you:

• Have a fever
• Lose weight
• Pass blood in your stools
• Feel tired all time
• Have a family history of bowel disorders or cancer
• Have abnormal results in your physical exam or blood tests.

If you don't have any of these alarm signs and all your tests are negative, your doctor will probably diagnose IBS.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.