The Diagnosis of Colorectal Cancer
The first step in the diagnosis of colorectal cancer may be a "digital rectal exam." In this test, which is often part of a routine physical exam, the doctor inserts a gloved finger into the rectum to feel for abnormal growths and may test your stool for occult blood. If colorectal cancer is suspected, you and your doctor have many tests to choose from to make sure the diagnosis is correct. Since there is a wide range of options, knowing the differences can help you make a smart decision.
Before these tests (except the fecal occult blood test), your colon must be completely empty. To clean out your bowels before the procedure, you may be instructed to have an enema or drink a large volume of a liquid laxative prescribed by your doctor. This preparation is very important in ensuring the accuracy of the test.
Fecal occult blood test
In this simple, initial screening test for colorectal cancer, a stool sample is applied to a special card that turns color if any blood is detected.
Barium enema
A narrow tube is inserted into the rectum to allow liquid barium (a white, chalky liquid) into the colon. A special x-ray is then taken, on which tumors or masses appear as dark shadows. The barium makes it easier to see the tumors. Before this test, you will be told to fast (not eat or drink) for several hours.
Flexible sigmoidoscopy
A thin, lighted tube inserted into the rectum allows the doctor to look into the rectum and first section of the colon (where half of all polyps are found).
Colonoscopy
The most accurate and thorough test for colorectal cancer. A long, thin, lighted tube inserted into the rectum allows the doctor to look into the entire colon, remove polyps, and take tissue for biopsy. Polyp removal will prevent cancer from developing. A mild sedative is usually given with this test.
Ultrasound
This noninvasive test uses images and sound waves to take a picture of the inside of the body. Unusual patterns in this image can indicate a mass or tumor. This test is used primarily to find cancer that has already spread to other organs.
Virtual colonoscopy (CT colonography)
This test creates a 3-dimensional reconstruction of the colon to reveal any abnormal masses. Images are taken seconds after the colon is inflated with carbon dioxide through a small rectal tube. Virtual colonoscopy is a fairly new technology, so it is not yet clear how accurate it is.
Colon cancer is often well advanced when it is detected. That's why the American Cancer Society recommends some kind of screening test on a regular basis after the age of 50.
