Structure of the colon
There are multiple methods available to examine the structure of the colon. One method uses a contrast material that can be seen on x-ray (barium enema) to outline the anatomy of the colon. A barium enema consists of the injection of radiation-dense barium through the anus into the colon. The doctor may then see the colon outline on x-ray films.
Sigmoidoscopy or colonoscopy
Other methods use a thin flexible tube with a video camera at its tip; the tube is slowly inserted into the rectum and lets a doctor view the inside of the rectum and colon (sigmoidoscopy or colonoscopy). In colonoscopy an image of the entire large bowel, or colon, is relayed through the instrument onto a video screen. Sigmoidoscopy is a similar test, but only the left side of the colon is seen. For a sigmoidoscopy, sedation is seldom given. The procedure is uncomfortable, even painful, but is usually brief. On the other hand, colonoscopy requires sedation. You are not put to sleep since you need to be conscious and cooperative throughout (conscious sedation). Sedation lessens the inevitable anxiety associated with the test and, when given with a painkiller, it reduces the pain. You may even forget having had the test.
Colonic transit time (Sitzmark) study
A colonic transit time (Sitzmark) study is a simple but effective method of studying how well the bowel propels food along. Normally, it takes only a little time for food that is eaten to progress through the small intestine into the colon. It then may take longer periods for the remaining material to pass through the colon and to be expelled as stool. There are several ways of performing the study. In some laboratories, for example, three capsules containing small markers are swallowed, one on each of three successive mornings (Days 1, 2 & 3). On the following day (Day 4) and three days later (Day 7) a plain x-ray of the abdomen is taken. All of the markers seen on the x-rays of each day are counted and added together. This number is the total transit time. This test is very useful for detecting different types of constipation.
Scintigraphic emptying and transit
Scintigraphic or nuclear medicine studies may be performed by labeling a material with a low-grade nuclear isotope and then following the progress of the material through the intestine. The emissions from the isotope are picked up by a special camera and the data is analyzed by a computer. The radiation dose is very small, even compared with standard contrast x-rays. This technology may be used to evaluate emptying of the stomach, transit through the intestines or emptying of the rectum.
It is usually not necessary to perform tests to document the motility disorder associated with diarrhea, but your doctor may want to collect a stool sample to evaluate other causes for diarrhea. A symptom diary in which you record the number of bowel movements and rate their consistency (watery, loose, formed, etc.) for 1-2 weeks can be very helpful to your doctor in deciding on the most appropriate treatment. [IFFGD has a Personal Daily Diary available that is designed specifically for gastrointestinal disorders.]
Adapted from IFFGD Publication: Colonoscopy and Sigmoidoscopy: What to Expect by W. Grant Thompson, MD, FRCPC, Emeritus Professor of Medicine, University of Ottawa, Ontario, Canada, IFFGD Publication #111 by Bruce A. Orkin, MD, Division of Colon and Rectal Surgery, The George Washington University, Washington, DC, and IFFGD Publication #162 by William Whitehead, PhD, Co-Director, Center for Functional GI & Motility Disorders Center Professor of Medicine, Division of Digestive Diseases Professor of Psychology University of North Carolina, Chapel Hill, NC.