IBD, Medical Tests

Tests to Detect Colorectal Cancer

What methods are used to screen people for colorectal cancer? 

Several screening tests have been developed to help doctors find colorectal cancer before symptoms begin, when it may be more treatable. Some tests that detect adenomas and polyps can prevent the development of cancer because these tests allow growths that might otherwise become cancer to be detected and removed. Colorectal cancer screening may be a form of cancer prevention in addition to early detection. 

The US Preventive Services Task Force (USPSTF) considers the following methods to be acceptable screening tests for colorectal cancer. 

Stool tests 

Both polyps and colorectal cancers can bleed, and stool tests check for tiny amounts of blood in feces (stool) that cannot be seen visually. (Blood in stool may also indicate the presence of conditions that are not cancer, such as hemorrhoids. If you are curious about other tests that can be detected from a stool test, talk to your provider or Care Team)  
Currently, three types of stool tests are approved by the US Food and Drug Administration (FDA) to screen for colorectal cancer: guaiac FOBT (gFOBT); the fecal immunochemical (or immunohistochemical) test (FIT, also known as iFOBT); and multitargeted stool DNA testing (also known as FIT-DNA).  

With these tests, stool samples are collected by the patient using a kit, and the samples are returned to the doctor. People who have a positive finding with these tests are advised to have a colonoscopy. 

  • gFOBT uses a chemical to detect heme, a component of the blood protein hemoglobin. Because the gFOBT can also detect heme in some foods (for example, red meat), people must avoid certain foods before having this test. 
  • FIT uses antibodies to detect hemoglobin protein specifically. Dietary restrictions are typically not required for FIT. 
  • FIT-DNA detects hemoglobin, along with certain DNA biomarkers. The DNA comes from cells in the lining of the colon and rectum that are shed and collect in stool as it passes through the large intestine and rectum.  

These three different tests have been shown to have different strengths and weaknesses. To find out what kind of stool test may work best for you, speak with your provider or a member of your Care Team. 


In this test, the rectum and sigmoid colon are examined using a sigmoidoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. This instrument is inserted through the anus into the rectum and sigmoid colon as air is pumped into the colon to expand it so the doctor can see the colon lining more clearly. 

During a sigmoidoscopy, abnormal growths in the rectum and sigmoid colon can be removed for analysis (biopsied). The lower colon must be cleared of stool before sigmoidoscopy, but the preparation is not very extensive. People are usually not sedated for this test. 
Clinical trials have shown that having sigmoidoscopy lowers the risks of developing and dying from colorectal cancer. Experts generally recommend sigmoidoscopy every 5 or 10 years for people at average risk who have had a negative test result. People who are screened with sigmoidoscopy may also be tested every few years with FIT, one of the stool tests, one of the stool tests.  


In this test, the rectum and entire colon are examined using a colonoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. Like the shorter sigmoidoscope, the colonoscope is inserted through the anus into the rectum and the colon as air is pumped into the colon to expand it so the doctor can see the colon lining more clearly.  

During a colonoscopy, any abnormal growths in the entire colon and the rectum can be removed. Preparation for colonoscopy requires a thorough cleansing of the entire colon before the test. Most patients receive some form of sedation during the test. 
A meta-analysis of six observational studies reported that screening with colonoscopy substantially reduces the risks of developing and dying from colorectal cancer. Experts recommend colonoscopy every 10 years for people at average risk as long as their test results are negative. observational studies reported that screening with colonoscopy substantially reduces the risks of developing and dying from colorectal cancer. Experts recommend colonoscopy every 10 years for people at average risk as long as their test results are negative.  

Virtual colonoscopy 

Also called computed tomographic (CT) colonography, is a screening method that uses special x-ray equipment (a CT scanner) to produce a series of pictures of the colon and the rectum from outside the body. A computer then assembles these pictures into detailed images that can show polyps and other abnormalities.  

As with standard colonoscopy, a thorough cleansing of the colon is necessary before this test. If polyps or other abnormal growths are found during a virtual colonoscopy, a standard colonoscopy must usually be performed to remove them.  
Because virtual colonoscopy also produces images of areas outside the colon and rectum it can lead to the unintentional discovery of medical findings in these areas that require additional follow-up procedures. Virtual colonoscopy may also miss small polyps. However, many small polyps may not be likely to become cancer and so taking them out may not be of benefit.  

Other methods 

Several other tests to screen for colorectal cancer exist, including blood-based DNA tests (liquid biopsy), double-contrast barium enema (DCBE), and single-specimen gFOBT done in a doctor’s office. However, these are not generally recommended.  

Considerations for IBD  

Many people with IBD may have experience with a colonoscopy. Have a discussion with your provider or Care Team about past experiences and any questions or concerns you may have about a future colonoscopy. 

What do colorectal cancer screening guidelines say about who should have colorectal cancer screening? 

Expert medical groups, including the US Preventive Services Task Force (USPSTF), strongly recommend screening for colorectal cancer. Although some details of the recommendations vary, most groups generally recommend that people at average risk of colorectal cancer get screened at regular intervals beginning at age 50, although the American Cancer Society recommends that routine screening begins at age 45. 

USPSTF recommends that screening continues to age 75; for those aged 75–85 years, the decision to screen is based on the patient’s life expectancy, health status, comorbid conditions, and prior screening results.  

People who are at increased risk of colorectal cancer because of a family history of colorectal cancer or documented advanced polyps or because they have certain chronic illnesses may be advised to start screening earlier and/or have more frequent screening. 

Speak with your doctor or a member of your Care Team about whether your chronic condition may require you to have more frequent screenings. 

How can people and their health care providers decide which colorectal cancer screening test(s) to use?  

It is important to have colorectal cancer screening. Different tests have different advantages and disadvantages, and people should talk with their health care provider or a member of their Care Team about which test is best for them. 

An individual’s decision about which test to have may depend on: 

  • The person’s age, medical history, family history, and general health 
  • Potential harms of the test 
  • The preparation required for the test 
  • Whether sedation may be needed for the test 
  • The follow-up care needed after the test 
  • The convenience of the test 
  • The cost of the test and the availability of insurance coverage 

The table below summarizes key features of the different colorectal screening tests that people may want to consider when choosing a test.  

Stool tests Sigmoidoscopy Colonoscopy Virtual colonoscopy 
Diet and medication changes before test? Yes, for gFOBT, no for FIT or FIT-DNAYes Yes No 
Invasive procedure? No Yes Yes No 
Preparation (colon cleansing) needed? No Yes (less extensive than for colonoscopy) Yes Yes 
Sedation needed? No Usually no Yes No 
Test frequency Every year to every 3 years, depending on the test Every 5 to 10 years, possibly with more frequent FIT Every 10 years Every 5 years 
Additional considerations Follow-up colonoscopy will likely be needed if test is positive Abnormal tissue can be removed during exam 
Very small risk of tearing or perforation of the lining of the colon 
Not widely available in United States (20) 
Abnormal tissue can be removed during exam 
Small risk of tearing or perforation of the lining of the colon 
Follow-up colonoscopy will likely be needed if test is positive 
Not widely available and may not be covered by insurance 
Can find abnormalities outside the colon that may need follow-up 
Involves exposure to a small amount of radiation 

What happens if a colorectal cancer screening test finds an abnormality? 

If a screening test finds an abnormality (a lesion or tumor), additional tests may be needed. These tests most often include a colonoscopy if it has not already been done, such as in the case of stool blood testing.  

If an abnormality is found during sigmoidoscopy, a biopsy or polypectomy may be performed during the test, and a follow-up colonoscopy may be recommended.  

If an abnormality is found during a standard colonoscopy, a biopsy or polypectomy may be performed during the test to determine whether cancer is present. If an abnormality is detected during a virtual colonoscopy, the patient will be referred for a standard colonoscopy. 

Source: National Cancer Institute