Diagnosing constipation

Generally, constipation can be confirmed from symptoms and medical history. In other words, no tests or procedures have to be performed.

Symptoms

Your doctor will ask questions about:

• The nature of your symptoms (duration and characteristics)
• Your bowel habits
• Your diet
• Laxative use 
• Your level of exercise
• Any recent change in your routine
• Whether there is a family history of bowel disturbance
• Whether you experience emotional distress and/or affective disorders

Physical examination

The doctor will also perform an abdominal examination. You’ll lie on your back, while the doctor feels your lower abdomen. 

If your practitioner thinks you may have faecal impaction (when dry, hard stools collect in your rectum), he or she may carry out a digital rectal examination. Typically, for this examination, your doctor will ask you to lie on your side while he or she uses a lubricated, gloved finger to feel for any stools that may have collected. 

With children a digital rectal examination is generally unnecessary, as the diagnosis can usually be made by feeling the child’s stomach.

Your doctor may also use the following tests and procedures to diagnose chronic constipation (and to try to find the cause):

• Blood tests. Your doctor will look for a systemic condition to rule out any other conditions. For example, he or she may test your thyroid function, and do glucose and electrolyte tests.
• Colonoscopy and sigmoidoscopy. These tests are done to determine if there are any obstructions. This is an examination of the entire colon or of the rectum and lower (sigmoid) colon. A lighted, flexible, camera-equipped tube is inserted into your anus to examine your rectum and colon.
• Anorectal manometry. This is an evaluation of anal sphincter muscle function. A small device with a balloon at one end is inserted into the anus and rectum. The balloon is inflated and pulled back through the sphincter muscle. This procedure allows your doctor to measure how well the muscles and nerves in and around your rectum function. 
• Balloon expulsion test. This test involves the evaluation of anal sphincter muscle speed. Often used along with anorectal manometry, this test measures the amount of time it takes for you to push out a balloon that’s been filled with water and placed in your rectum.
• Ano-rectal motility studies. This is the assessment of the function of the muscles and nerves of the anus and rectum. A flexible tube is inserted through the anus and into the rectum. Sensors within the tube measure the pressures that are generated by the muscles of the anus and rectum. With the tube in place, you perform several simple movements such as voluntarily tightening of the anal muscles. These studies help to determine if the muscles of the anus and rectum are working normally.
• Abdominal X-ray. X-ray radiation is used to produce images of the inside of your abdomen. The stool inside the colon is visible on an X-ray.
• Barium enema. Liquid barium is inserted through the anus to fill the rectum and colon. The barium outlines the colon on the X-rays and defines the normal or abnormal anatomy of the bowel and rectum. 
• Colonic transit study. This involves the evaluation of how well food moves through the colon. A capsule that contains either a radiopaque marker or a wireless recording device is swallowed. The progress of the capsule through your colon is then recorded over several days and is visible on X-rays. 
• Scintigraphy. This is another colonic transit study where radiocarbon-activated food is eaten and a special camera is used to record the progress of the food. Your doctor will look for signs of intestinal muscle dysfunction and how well food moves through your colon.
• Defecography. During this test, an X-ray is taken of the rectum during defecation. A soft paste made of barium is inserted into your rectum. You then pass the barium paste as you would a stool. The barium shows up on X-rays and may reveal a prolapse or problems with muscle function and muscle coordination.                       
• MRI defecography. Contrast gel is inserted into your rectum. You then pass the gel, and the MRI scanner can visualise and assess the function of the defecation muscles. This test can also diagnose problems that can cause constipation, such as rectocele (posterior vaginal prolapse) or rectal prolapse.

Read more:
Treating constipation

Reviewed by Kim Hofmann, registered dietitian, BSc Medical (Honours) Nutrition and Dietetics, BSc (Honours) Psychology, December 2017.