What diagnostic tests are used for constipation?
Most people with constipation do not need extensive testing and can be treated with changes in diet and exercise. For example, in young people with mild symptoms, a medical history and physical examination may be all the doctor needs to suggest successful treatment. The tests the doctor performs depend on the duration and severity of the constipation, the person's age, and whether blood in stools, recent changes in bowel movements, or weight loss have occurred.
The doctor may ask a patient to describe his or her constipation, including duration of symptoms, frequency of bowel movements, consistency of stools, presence of blood in the stool, and toilet habits (how often and where one has bowel movements). A record of eating habits, medication, and level of physical activity or exercise will also help the doctor determine the cause of constipation.
The clinical definition of constipation is any two of the following symptoms for at least 12 weeks (not necessarily consecutive) in the previous 12 months:
- straining during bowel movements
- lumpy or hard stool
- sensation of incomplete evacuation
- sensation of anorectal blockage/obstruction
- fewer than three bowel movements per week
A physical exam may include a rectal exam with a gloved, lubricated finger to evaluate the tone of the muscle that closes off the anus (anal sphincter) and to detect tenderness, obstruction, or blood. In some cases, blood and thyroid tests may be necessary to look for thyroid disease and serum calcium or to rule out inflammatory, neoplastic, metabolic, and other systemic disorders.
Extensive testing usually is reserved for people with severe symptoms, for those with sudden changes in number and consistency of bowel movements or blood in the stool, and for older adults. Additional tests that may be used to evaluate constipation include
- colorectal transit study
- anorectal function tests
Because of an increased risk of colorectal cancer in older adults, the doctor may use tests to rule out a diagnosis of cancer, including
- barium enema x ray
- sigmoidoscopy or colonoscopy
Colorectal transit study. This test, reserved for those with chronic constipation, shows how well food moves through the colon. The patient swallows capsules containing small markers that are visible on an x ray. The movement of the markers through the colon is monitored with abdominal x rays taken several times 3 to 7 days after the capsule is swallowed. The patient follows a high-fiber diet during the course of this test.
Anorectal function tests. These tests diagnose constipation caused by abnormal functioning of the anus or rectum (anorectal function). Anorectal manometry evaluates anal sphincter muscle function. For this test, a catheter or air-filled balloon inserted into the anus is slowly pulled back through the sphincter muscle to measure muscle tone and contractions.
Defecography is an x ray of the anorectal area that evaluates completeness of stool elimination, identifies anorectal abnormalities, and evaluates rectal muscle contractions and relaxation. During the exam, the doctor fills the rectum with a soft paste that is the same consistency as stool. The patient sits on a toilet positioned inside an x ray machine and then relaxes and squeezes the anus to expel the paste. The doctor studies the x rays for anorectal problems that occurred as the paste was expelled.
Barium enema x ray.This exam involves viewing the rectum, colon, and lower part of the small intestine to locate any problems. This part of the digestive tract is known as the bowel. This test may show intestinal obstruction and Hirschsprung's disease, a lack of nerves within the colon.
The night before the test, bowel cleansing, also called bowel prep, is necessary to clear the lower digestive tract. The patient drinks a special liquid to flush out the bowel. A clean bowel is important, because even a small amount of stool in the colon can hide details and result in an incomplete exam.
Because the colon does not show up well on x rays, the doctor fills it with barium, a chalky liquid that makes the area visible. Once the mixture coats the inside of colon and rectum, x rays are taken that reveal their shape and condition. The patient may feel some abdominal cramping when the barium fills the colon, but usually feels little discomfort after the procedure. Stools may be a whitish color for a few days after the exam.
Sigmoidoscopy or colonoscopy. An examination of the rectum and lower (sigmoid) colon is called a sigmoidoscopy. An examination of the rectum and entire colon is called a colonoscopy.
The patient usually has a liquid dinner the night before a sigmoidoscopy and takes an enema early the next morning. A light breakfast and a cleansing enema an hour before the test may also be necessary.
To perform a sigmoidoscopy, the doctor uses a long, flexible tube with a light on the end called a sigmoidoscope to view the rectum and lower colon. First, the doctor examines the rectum with a gloved, lubricated finger. Then, the sigmoidoscope is inserted through the anus into the rectum and lower colon. The procedure may cause a mild sensation of wanting to move the bowels and abdominal pressure. Sometimes the doctor fills the colon with air to get a better view. The air may cause mild cramping.
To perform a colonoscopy, the doctor uses a flexible tube with a light on the end called a colonoscope to view the entire colon. This tube is longer than a sigmoidoscope. The same bowel cleansing used for the barium x ray is needed to clear the bowel of waste. The patient is lightly sedated before the exam. During the exam, the patient lies on his or her side and the doctor inserts the tube through the anus and rectum into the colon. If an abnormality is seen, the doctor can use the colonoscope to remove a small piece of tissue for examination (biopsy). The patient may feel gassy and bloated after the procedure.