Types of screening tests

Many tests can be used to screen for colorectal cancer. Some of them also allow your provider to find and remove precancerous polyps at the same time.

Visual exams to find colorectal polyps and cancer

• Colonoscopy. This test looks at your rectum and your entire colon. It uses a colonoscope. This is a long, lighted tube with a tiny video camera on the end. The scope is put in through your rectum. The healthcare provider looks for polyps or other abnormal areas as the scope passes through your colon. These can be taken out through the scope and sent to a lab for testing. You are given medicine to make you sleep and not feel pain during this test. A colonoscopy is the only test that lets the provider see the entire colon and rectum and remove pieces of any abnormal areas for testing. If you have any of the other tests and something is found, you will likely need a colonoscopy. 

• Flexible sigmoidoscopy. This test looks at your rectum and the lower part of your colon. Your healthcare provider puts a thin, lighted tube with a tiny video camera on the end into your rectum. The tube is called a sigmoidoscope. The process is the same as with colonoscopy, but the scope doesn't go in as far. It only looks at your sigmoid colon just past the rectum. Your provider looks for polyps or other abnormal areas. These can be removed and sent to a lab for testing. Colonoscopy is more common in the U.S. because the entire colon can be checked.

• Virtual colonoscopy (CT colonography). This test is a special type of CT scan of the colon and rectum. Once the CT images are taken, a computer combines them to create a 3-D picture. This lets the provider look for polyps or cancer. This test doesn't allow for simultaneous biopsies so if an abnormality is seen, you will have to prep for a colonoscopy (see above).

Stool-based tests

These tests look for signs of cancer in your stool or feces. These tests can be done at home. But they are less likely to find polyps. And they must be done more often than the tests above:

• Fecal occult blood test (FOBT) or fecal immunochemical test (FIT).  These tests look for hidden (occult) blood in the stool. Blood vessels in cancer tumors and sometimes in polyps are easily broken during a bowel movement. This may cause blood to show up in your stool. For these tests, you collect a small amount of your stool with a brush or wooden applicator. Then you smear it on a special card that can find blood. In most cases, you need to do this for a few bowel movements in a row. You then send the cards to your healthcare provider’s office or to a lab.

• Stool DNA test. This test looks for DNA changes in cells in the stool that might be signs of cancer. It also looks for hidden blood in stool. For this test, you collect an entire bowel movement. This is done by putting a special container in the toilet. The stool is sent to a lab for testing. Your provider will give you a kit and directions on how to do this test at home.

Blood tests

There are blood tests available that look for signs of colorectal cancer or pre-cancerous polyps. A sample of your blood is taken in a clinic and tested in a lab. You don't need to do any bowel prep before this test. If you have abnormal results, you will likely need a colonoscopy.

What expert groups advise

The American Cancer Society and U.S. Preventive Services Task Force advise people at average risk for colorectal cancer start screening at age 45. This is because of an increase of colorectal cancer in people younger than age 50. How often you need these screening tests depends on which test you have.

Screening for those who are age 45 and of average risk for colorectal cancer include one of the following choices:

• A colonoscopy every 10 years, or

• A flexible sigmoidoscopy every 5 years (or every 10 years with yearly FIT stool test), or

• A CT colonography (virtual colonoscopy) every 5 years, or

• A fecal occult blood test (FOBT) or fecal immunochemical test (FIT) every year

• A stool DNA test every 1 to 3 years

Regular colorectal cancer screening for those at average risk continues through age 75 for people in good health and a life expectancy of 10 years or more. For people ages 76 to 85, talk with your healthcare provider about continued screening. Screening for people older than 85 is not advised.

Average vs. high risk

Most people are at average risk and should follow advice like those listed above. But some people are at higher risk for colorectal cancer based on things like:

• A personal or family history of colorectal cancer

• Precancerous polyps found on previous biopsies

• They have or might have certain inherited syndromes, such as familial adenomatous polyposis (FAP), and Lynch syndrome or hereditary nonpolyposis colon cancer

• A personal history of inflammatory bowel disease such as Crohn's or ulcerative colitis

• They were treated with radiation to the belly (abdomen) or pelvis in the past

These people might need to start screening at a younger age. They also may need to be screened more often. For instance, if certain types of polyps are found on your colonoscopy, you may need to get another colonoscopy in the next 3 to 5 years instead of waiting 10 years.

Talk with your healthcare provider

It's important to know your risk. Talk with your provider about your risk for colorectal cancer, when you should start screening, and which tests might be right for you. Also talk with your health insurance carrier to know which tests are covered by your insurance.

No matter which test you choose, the most important thing is that you get screened and that screening is done at the right time interval. Keep in mind that you can save yourself from future surgeries and treatments with serious side effects by preventing colorectal cancer or finding it early with these well-established screening tests.