Colorectal cancer screening looks for cancer at the earliest stages, when it's most treatable. It can find colorectal polyps (growths on the colon’s or rectum’s inner lining) before they become cancerous or find cancer before it spreads. Screening can save your life, so follow your doctor’s screening recommendations.
Screening tests either check your stool or use imaging equipment to look inside your colon and rectum for signs of cancer. Your doctor will discuss which tests are right for you based on your personal and family health history and risk factors.
The Affordable Care Act (ACA) requires private insurers and Medicare to cover the costs of colorectal cancer screening tests with no out-of-pocket costs to patients. But insurance providers have different coverage requirements, such as age, test type, and frequency. Check with your insurance provider to find out what’s covered under your policy.
Fecal occult blood test (FOBT)
This test finds blood in the stool, which may signal colon cancer or other problems like polyps. Larger colorectal polyps or cancers have bigger, more fragile blood vessels that can be damaged during a bowel movement. This can cause them to bleed into the colon or rectum and the stool, but not enough to see with the naked eye.
You receive a kit from your doctor's office or a lab with all the supplies and instructions, do it at home, and then mail it back. The test is easy to do, but it must be done every year. It can’t tell your doctor where the blood is coming from, such as stomach ulcers or hemorrhoids, and it can only detect polyps that bleed (large polyps). If blood is found, you’ll need to have a colonoscopy to find out what’s causing bleeding.
There are two types of FOBT:
- Guaiac-based (gFOBT). This method uses a card that tests a few stool samples. Some foods and medicines can cause inaccurate results, such as red meat, pain relievers, and vitamin C. Talk to your doctor about any medicines or supplements you’re taking and which foods you should avoid before the test.
- Immunochemical test (FIT). This test, which uses a collection container, is usually preferred over the gFOBT because it’s better at detecting colon cancer, and there aren’t any dietary restrictions before the test. The FIT is also less likely to react to bleeding in the stomach or other areas of the upper digestive tract.
Stool DNA testThis test looks at the DNA from a stool sample for changes that occur in polyps or cancer, and it also can detect blood in the stool. Like FOBT, this test includes a kit with supplies and instructions that you complete at home and mail back. It tests a full stool sample, and there aren’t any food or drug restrictions necessary before the test. It’s done every three years. If it finds DNA changes or blood in the sample, you’ll need to have a colonoscopy to take a closer look.
This test uses a colonoscope – a thin, flexible, lighted tube with a video camera – inserted into your anus to look inside your rectum and the full length of your colon. Before doing the test, air is pumped into your colon to make it easier for your doctor to see the inner lining. During the test, your doctor can use the colonoscope to remove or take samples (biopsies) of polyps or other precancerous growths using tiny instruments. Biopsy results are usually available within a few days.
Your colon and rectum need to be empty so that your doctor can see the inner lining clearly during the test. That means you need to prepare the day before – called bowel prep. There are various ways to do this, such as using medicine, fluids, enemas, or a combination of these. And, you’ll need to stop eating and drinking after a certain point the night before your test. Your doctor will explain all your bowel prep options and eating, drinking, and medicine restrictions before the test.
You receive medicine to relax you during the test and keep you comfortable. After the test, your care team will keep an eye on you for up to an hour as the medicine wears off. You’ll feel groggy after the test, so you must have someone pick you up afterward. Your care team will discuss your results with you and your friend or family member and give you instructions about what you can and can't do after the test.
Most people may feel bloated or have cramps from air that’s pumped into the colon during the test. These go away once the air passes out of your body.
Colonoscopies rarely cause complications, which can include:
- Bleeding in the area where a tissue sample is taken or a polyp is removed
- Reaction to the medicine used to relax you during the test
- Tearing in the wall of the colon or rectum
People at average risk of colorectal cancer should have a colonoscopy every 10 years. If you’re at greater risk, your doctor may recommend more frequent testing.
CT colonography, also called virtual colonoscopy, examines the rectum's and colon’s inner lining using computed tomography (CT). This imaging equipment creates 3D images of the inside of your rectum and colon without using a colonoscope. You still need to use the same bowel prep procedure as you would before a colonoscopy to clear and empty your bowel, but you are fully awake during the test, and you don’t need medicine to relax you.
Your doctor inserts a small tube into your rectum and gently inflates the colon with air to make it easier to inspect the lining during the test. The scan can be done quickly – usually in about 30 minutes – which offers an option for people who can’t or choose not to have a more invasive colonoscopy. But if your doctor finds a polyp or an area the needs further inspection, it can’t be removed or biopsied since the test doesn’t use any instruments. You would need a colonoscopy to examine the area more closely.
You may feel bloated or have cramps from the air in your colon, but it goes away once the air passes out of your body. Since this is a CT scan, you're exposed to a small amount of radiation. There’s a minimal risk that the colon could tear when it’s being inflated with air.
Colorectal Screening Resources
- American Cancer Society
- Centers for Disease Control and Prevention (CDC)
- U.S. Preventive Services Task Force