When the symptoms of colon cancer occur, a prompt diagnosis is required, according to the American Society of Colon and Rectal Surgeons. Because there may be few symptoms of colon cancer until the disease has progressed, routine screening is recommended after the age of 50, according to the National Cancer Institute. A colonoscopy is the screening test most often used. Depending on the patient’s symptoms, doctors use a variety of tests to diagnose colon cancer after symptoms are present.
Digital Rectal Examination
In addition to a full physical examination and history, the doctor usually does a digital rectal examination. By inserting a lubricated, gloved finger into the rectum, the area is explored manually. Samples of the feces in the rectum are collected. Colon cancer is not usually found with this examination, but hemorrhoids or other problems may be discovered.
Fecal Occult Blood and DNA Tests
Colon cancer often grows from a polyp in the lining of the intestine. A polyp or tumor may bleed and cause blood in the bowel movement. A fecal occult blood test involves placing a small bit of feces on a chemically treated pad. A reaction or color change shows the presence of even minute amounts of blood. Other conditions such as hemorrhoids can cause a reaction so if blood is present, additional tests are needed. There are also tests for DNA in the stool that indicate the presence of cancer cells. These tests are not widely available but their use is increasing.
Colonoscopy and Sigmoidoscopy
A colonoscopy may be ordered to explore the cause of bleeding or abdominal distention. A colonoscopy is usually done as a screening test for colon cancer or to investigate symptoms. Using a lighted tube with a camera, the doctor inserts the colonoscope into the rectum and threads it through the colon. Small polyps may be removed to test for signs of cancer, but larger polyps or a tumor will need surgery.
A sigmoidoscopy is similar to a colonoscopy, but only the rectum and lower part of the colon are viewed so it is used less often. Polyps are removed and sent to be tested for cancer cells. Drugs that relax and/or anesthetize the patient may be used to make the procedures more comfortable.
Virtual Colonoscopy
Using radiology tests, pictures of the inside of the colon are viewed by a doctor for visible signs of colon cancer. With computerized tomography, CT, or magnetic resonance imaging, MRI, a three-dimensional image is constructed of the colon. The colon is inflated with carbon dioxide for the CT and contrast medium, a liquid that shows up on X-rays, may be used with the MRI. The tests take about 10 minutes. There are advantages and disadvantages to virtual colonoscopy. No sedation is needed and blockages in the colon are easily viewed. One disadvantage is that polyps can not be removed during the procedure.
Barium Enema
Another radiology test that may be used is a double-contract barium enema. Barium, a liquid used to enhance the pictures obtained from X-rays, is given with an enema and then air is blown into the rectum. Pictures of the colon and rectum are taken that will show polyps or tumors.
