What happens during a colorectal cancer screening?
There are two main types of colorectal cancer screening tests: visual exams and stool tests. There are different options for both types of tests.
Visual exams are procedures that allow a provider to look inside the colon and rectum. They are done either using a thin tube with a camera attached or with a special imaging device. Types of visual exams include:
Colonoscopy. This test allows a provider to view your entire colon and rectum. It is often done in an outpatient department of a hospital or medical center. Before the test, you will need to empty out your colon (large bowel) in a procedure called bowel prep. During the test:
- You will lie on an exam table.
- You will be given medicine called a sedative to help you relax. It also prevents you from feeling pain during the procedure. You may be awake for the test, but you probably won’t remember anything.
- A colonoscope, a thin, lighted tube with a camera attached, will be inserted into your rectum and up into your colon.
- Your provider will look for colorectal polyps or other abnormal areas.
- Your provider may remove polyps or tissue samples using special tools inserted through the scope.
- Polyps or samples may be sent to a lab for testing.
The sedative you are given may make you drowsy for several hours. You should arrange for someone to drive you home.
Sigmoidoscopy. This test allows your provider to look at the lower part of the colon. During the test:
- You will lie on an exam table with your knees drawn up to your chest.
- A sigmoidoscope, a flexible, lighted tube with a camera, will be inserted into the rectum and up into the lower part of the colon.
- Air will be pumped through the sigmoidoscope to make the colon bigger and easier to see.
- The air may make you feel like you need to have a bowel movement or pass gas.
- Your provider may remove polyps or tissue samples using special tools inserted through the scope.
- Polyps or samples may be sent to a lab for testing.
Virtual Colonoscopy. This is a type of x-ray that uses a CT scan (computed tomography) to take detailed, 3-dimensional pictures of the entire colon and rectum. It is usually done in a radiology department of a hospital or medical center. This procedure also requires bowel prep beforehand. During the test:
- You will lie on a narrow table.
- You may be asked to drink a liquid containing contrast dye. Contrast dye is a substance that makes parts of your body show up more clearly on an x-ray.
- A provider will insert a small tube into the rectum.
- Air will be pumped through the tube to make the colon bigger and easier to see.
- The table will slide into the CT machine.
- A series of images will be taken.
Stool tests look at stool samples for signs of cancer. For these tests, you take a stool sample at home and send it to a lab. Types of stool tests:
Fecal occult blood tests. These tests look for hidden (known as occult) blood in the stool. Blood in the stool may be a sign of polyps, cancer, or other conditions. Your health care provider will give you a kit that includes instructions on how to do the test.
There are two types of fecal occult blood tests: the fecal immunochemical test (FIT) and the guaiac smear method (gFOBT). Below are typical instructions for each test. Your instructions may vary slightly depending on the manufacturer of the test kit.
For a fecal immunochemical test (FIT), you will most likely need to:
- Collect samples from two or three separate bowel movements.
- Collect the sample from the toilet using the special brush or other device included in your kit.
- For each sample, use the brush or device to take the sample from the surface of the stool.
- Brush the sample onto a test card.
- Label and seal all your samples as directed.
- Mail the samples to your health care provider or lab.
For a guaiac smear test (gFOBT), you will most likely need to:
- Collect samples from three separate bowel movements.
- For each sample, collect the stool and store it in a clean container. Make sure the sample does not mix in with urine or water from the toilet.
- Use the applicator from your test kit to smear some of the stool on the test card or slide, also included in your kit.
- Label and seal all your samples as directed.
- Mail the samples to your health care provider or lab.
Stool DNA test. This test checks for genetic changes in the stool that may be signs of colorectal polyps or cancer. Your provider will let you know to get a test kit. The kit will include instructions on how to do the test. The instructions will likely include the following steps:
- Put a special container inside your toilet.
- Collect an entire bowel movement.
- Close and seal the container.
- Mail the container with the stool sample to a lab for testing.