To find the cause of symptoms, the doctor will ask about your personal and family medical history. He will do a physical exam, and may order laboratory tests. In addition to the exams discussed above, the doctor may also order the following tests:

• Lower GI series – X-rays of the colon and rectum (the lower gastrointestinal tract). The x-rays are taken after the patient is given an enema with a white, chalky solution containing barium. (This test is sometimes called a barium enema.) The barium outlines the colon and rectum on the x-rays, helping the doctor find tumors or other abnormal areas. To make small tumors easier to see, the doctor may expand the colon by carefully pumping in air during the test. This is called an air contrast or double-contrast barium enema.
• Colonoscopy – An examination of the inside of the entire colon using a colonoscope, an instrument similar to a flexible sigmoidoscope, but longer.

If a polyp or other abnormal growth is found, the doctor can remove part or all of it through a sigmoidoscope or colonoscope. A pathologist examines the tissue under a microscope to check for cancer cells. This procedure is called a biopsy. Most polyps are benign, but a biopsy is the only way to know for sure.

If the pathologist finds cancer, the patient’s doctor needs to learn the stage, or extent of the disease. Staging exams and tests help the doctor find out whether the cancer has spread and, if so, what parts of the body are affected. Treatment decisions depend on these findings.

Staging may include x-rays, ultrasonography or CT (or CAT) scans of the lungs and liver, because colorectal cancer tends to spread to these organs. The doctor may order blood tests to measure how well the liver is functioning. The doctor also may do a blood test called a CEA assay. This test measures the blood level of carcinoembryonic antigen (CEA), a substance that is sometimes found in higher-than-normal amounts in people who have colorectal cancer, especially when the disease has spread.