Colon cancer is a type of cancer that starts in the lower intestine, or bowel. According to MayoClinic.com, colon cancer often originates from tiny growths that cause few detectable symptoms; therefore, doctors recommend regular testing for colon cancer--especially for those with a family history or other risk factors. Medical professionals use a variety of imaging and fecal tests to screen for colon cancer.
Colonoscopy
A colonoscopy is a test doctors use to examine the entire length of the colon for polyps, tumors, bleeding or other abnormalities, according to MedlinePlus. Prior to the test, patients typically must cleanse their bowels through the use of laxatives and restricted food intake. The doctor also routinely conducts a digital rectal exam, or DRE, a procedure in which the doctor inserts a gloved, lubricated finger into the rectum before beginning the colonoscopy. The purpose of the digital rectal exam is to ensure there are no blockages or other abnormalities in the rectum.
During the colonoscopy, the doctor inserts a colonoscope--a long tube with a camera on one end--through the rectum and into the colon. The camera transmits images of the inside of the large intestine to a monitor. Should the doctor find any suspicious tissue or growths, he can insert special tools into the colonoscope and remove them for biopsy.
Sigmoidoscopy
A sigmoidoscopy is a test that allows doctors to examine the lower section of the colon and rectum. According to MedlinePlus, during the procedure, a physician inserts a sigmoidoscope--a hollow, flexible, lighted tube with a camera attached to one end--into the rectum and carefully threads it into the lower bowel. After inserting air into the tube to expand the colon, the doctor carefully examines the structures and removes any suspicious growths for biopsy.
As with a colonoscopy, a sigmoidoscopy is usually preceded by a digital rectal exam and requires the bowel be empty before examination; therefore, physicians may ask patients to use an enema or laxative prior to the procedure, in addition to restricting intake of certain foods and liquids.
Blood and Stool Tests
The superficial blood vessels of polyps and tumors may rupture as feces pass through the colon, resulting in very small amounts of blood passing with the stool. According to the American Cancer Society, because the blood is not always detectable with the human eye, doctors sometimes ask patients to complete a fecal occult blood test--a screening procedure in which the patient collects stool samples at home and returns them to a medical lab or office for testing. By combining the feces with certain chemicals, the physician can test for the presence of hidden blood.
A newer version of this procedure called the fecal immunochemical test also tests for blood in the stool; however, it is more specific in that it tests for the presence of a particular protein found in red blood cells. Unlike the fecal occult blood test, the fecal immunochemical test is less likely to result in a false positive as a result of a patient's intake of certain foods or medications. According to the American Cancer Society, it is also less likely to react to blood in the stool coming from outside of the colon, in areas such as the stomach or esophagus.
MedlinePlus notes that doctors may also make use of an emerging test that can identify DNA abnormalities in the stool. Colon cancer causes abnormal changes to the genetic makeup of cells in the bowel. As patients excrete these cells in their stool, doctors can examine the feces for known genetic abnormalities associated with malignancy.
Double-Contrast Barium Enema
Doctors may use a specialized x-ray called a double-contrast barium enema to examine the entire colon. This test is also sometimes referred to as a "lower GI series" or "barium enema with air contrast," according to the American Cancer Society. During the test, the doctor injects air and barium sulfate--a chalk-like liquid that provides contrast in x-ray images--via an enema in the rectum. These substances expand and coat the inside of the rectum and colon to create a clear outline of the lower gastrointestinal tract. The doctor then takes x-rays to look for any suspicious growths.
Computerized Tomography Colonography
Sometimes referred to as virtual colonoscopy, computerized tomography (CT) colonography is a technically advanced imaging procedure that combines multiple two- and three-dimensional images of the colon, according to the American Cancer Society. After inserting air into the colon through a small tube in the rectum, the medical technician uses a CT scanner to take images of the colon while the patient is lying on his back and stomach. Some patients may drink a contrast dye to increase the level of detail on the images. According to MayoClinic.com, doctors may use this test on patients who are unable to undergo traditional colonoscopy.
