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If you have constipation, your doctor may order some tests to find out what's causing your symptoms.

But most people with constipation don't need any tests. You may have them if your doctor wants to make sure that your constipation isn't because of a more serious medical condition. You'll probably need them only if you have other symptoms as well as being constipated, such as bleeding or losing weight suddenly.

Some of the tests you might have are listed below.

• Blood test. You may have a blood test to check that your thyroid gland is working properly. The thyroid is a small gland in your neck. You can become constipated if your thyroid is underactive. To read more, see our information on Underactive thyroid.
• A test to see how much calcium you have in your blood. This test helps check for lots of different conditions. And it can give your doctor an idea of how healthy you are in general.
• Barium enema. This helps to take an X-ray of your bowel. A thick, white liquid that contains a chemical called barium is passed through a tube into your rectum. Barium shows up on X-rays, so it helps your doctor see if your bowel is blocked.
• Proctogram. This is a bit like a barium enema. You sit on a toilet in the X-ray room. X-rays are taken when you pass the barium in the same way as you would pass a stool.
• Colonoscopy. This test is done to check for disease inside your bowel. A doctor puts a tube with a camera on the end (a colonoscope) into your rectum and passes it into your colon. We've prepared some extra information for people thinking of having this test. To read more, see Colonoscopy.
• A test to measure how well your bowel muscles work. Your doctor may call this anorectal manometry. A thin tube with a balloon on its end is put into your rectum. The balloon is then slowly filled up. This makes the muscles in your rectum and anus squeeze, and a machine measures how strongly you squeeze. This test shows how well the muscles and nerves in your bowels are working. But this test isn't done often.
• A test that shows how well food moves through your bowels. For this test, you swallow some capsules that show up on X-rays. Your doctor can then find out how long it takes for food to pass through your body. But it's rare for people to need this test.

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.