Diagnosis of Constipation

How do doctors diagnose constipation?

Doctors diagnose constipation by

  • taking a medical history
  • performing a physical exam
  • performing diagnostic tests, such as a blood test

Medical history

The medical history will include questions about your constipation, such as

  • how often you have a bowel movement
  • how long you’ve had symptoms
  • what your stools look like and whether you have blood in your stool
  • your eating habits
  • your level of physical activity
  • the medicines you take
A doctor taking the medical history of a patient at a desk.
To find out why you have constipation, your doctor will take your medical history.

Physical exam

The physical exam may include a digital rectal exam. During a digital rectal exam, your doctor will have you bend over a table or lie on your side while holding your knees close to your chest. After putting on a glove, the doctor slides a lubricated finger into your anus to check for tenderness, blockage, or blood, and will ask you to squeeze your anal muscles.

Diagnostic tests

The tests your doctor may order for constipation depend on

  • how long you’ve been constipated
  • how severe your constipation is
  • your age
  • whether you’ve had blood in your stool, recent changes in your bowel movement pattern, or weight loss

What tests do doctors use to diagnose constipation?

A doctor may use one or more of the following tests to diagnose constipation.

Blood test

A health care professional may take a blood sample from you to test for certain conditions that can cause constipation, such as anemia or hypothyroidism.

Flexible sigmoidoscopy or colonoscopy

Although the tests are similar, doctors use a colonoscopy to view your rectum and entire colon, while they use a flexible sigmoidoscopy to view just your rectum and lower colon. For either procedure, you’ll lie on a table while your doctor inserts a flexible tube into your anus. A small camera on the tube sends a video image of your bowel lining to a monitor. The procedures can show signs of problems in your lower gastrointestinal (GI) tract.

During these two tests, your doctor may also perform a biopsy. The doctor may take several small pieces of tissue from different areas of your bowel lining. A pathologist will look at the tissue using a microscope. You won’t feel the biopsy.

A patient lying on their side while a doctor performs a colonoscopy and a depiction of the lower GI tract examined during a colonoscopy (including the colon, rectum, colonoscope, and anus.
Colonoscopy is used to view the entire colon and rectum. © October 2014 Terese Winslow LLC, U.S. Govt. has certain rights

Colorectal transit studies

Colorectal transit studies are tests that show how well stool moves through your colon.

  • Radiopaque markers. For this test, you swallow capsules with small radioactive markers that doctors can see on an x-ray. Three to 7 days after you swallow the capsules, a health care professional will take several x-rays of your abdomen that track the movement of the markers through your colon. You eat a high-fiber diet to help stool and the markers move through your GI tract. The markers pass when you have a bowel movement.
  • Scintigraphy. For this test, you eat a meal that contains radioactive substances. The dose of radioactive substances is small, so scintigraphy isn’t likely to damage your cells. A health care professional will use computers and special cameras placed outside your body over your abdomen to create pictures of the radioactive substances as they move through your intestines.

Anorectal function tests

Anorectal function tests can show problems in your anus or rectum.

  • Anal manometry uses pressure sensors and a balloon that a health care professional inflates inside your rectum to check how sensitive your rectum is and how well it works. Anal manometry also checks the tightness of the muscles around your anus and how well they respond to nerve signals. For this test, a health care professional puts a thin tube that has pressure sensors and a balloon on its tip into your anus. Once the balloon reaches your rectum and the pressure sensors are in your anus, the health care professional slowly pulls the tube out to measure muscle tone and contractions. The test takes about 30 minutes.
  • Balloon expulsion tests consist of a health care professional filling a balloon with different amounts of water after he or she places it into your rectum. The health care professional will give you a stopwatch and instructions to go to the restroom and measure the amount of time it takes you to push the balloon out. If you can’t push out a balloon filled with less than 150 milliliters of water, or it takes longer than 1 minute to push the balloon out, you may have a problem pushing out stool.

Lower GI series

A lower GI series is an x-ray exam that doctors use to look at your large intestine. A health care professional will perform the procedure at a hospital or an outpatient center. A health care professional may give you written instructions about what to do at home before the procedure, called a bowel prep.

The health care professional may ask you to follow a clear liquid diet for 1 to 3 days before the procedure. You may also need to use a laxative or an enema before the procedure. Laxatives and enemas cause diarrhea, so you should stay close to a bathroom during the bowel prep.

For the procedure, you’ll lie on a table while your doctor inserts a flexible tube into your anus. Your doctor then fills your large intestine with barium, which makes signs of problems that may be causing constipation show up more clearly on x-rays.

Traces of barium in your large intestine can cause white or light-colored stools for several days. Enemas and repeated bowel movements may cause anal soreness. A health care professional will give you specific instructions about eating and drinking after the procedure.

Defecography

Defecography is a video x-ray of the area around your anus and rectum. The procedure may show problems with how you have a bowel movement.

During the test, a health care professional fills your rectum with a soft paste that shows up on x-rays and feels like stool. You sit on a toilet next to an x-ray machine. The health care professional will ask you to first pull in and squeeze muscles to keep stool in. Then, he or she will tell you to strain to have a bowel movement. The health care professional looks for problems as you push the paste out.

Magnetic resonance imaging (MRI)

MRI machines use radio waves and magnets to produce detailed pictures of your body’s internal organs and soft tissues without using x-rays.

Patients don’t need anesthesia, although a health care professional may give light sedation, taken by mouth, to children and people with a fear of small spaces. A health care professional may inject a special dye, called contrast medium, into your body. In most cases, you’ll lie on a table that slides into a tunnel-shaped device. The tunnel may be open ended or closed at one end. A radiologist reviews the images. A doctor can use the MRI images to diagnose health problems that may be causing your constipation.

Computerized tomography (CT) scan

CT scans use x-rays and computer technology to create images. A health care professional may give you a solution to drink and an injection of contrast medium. You’ll lie on a table that slides into a tunnel-shaped device that takes the x-rays. Radiologists review the images. A doctor can use the MRI images to diagnose health problems that may be causing your constipation.

Patients don’t need anesthesia, although health care professionals may give children a sedative to help them fall asleep for the test.

Women of childbearing age should have a pregnancy test before having a CT scan. The radiation from CT scans can be harmful to a developing fetus.

November 2014
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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.