Colorectal cancer (CRC) is the fourth leading cause of death worldwide. Yet despite the ability of CRC screening to detect colon cancer early, and to find and remove potentially precancerous growths called polyps, screening rates remain low, below 60%. Experts generally agree that people should be screened for CRC at regular intervals beginning by age 50.
Colonoscopy is considered the gold standard for CRC screening. In this procedure, a doctor examines your entire colon through a colonoscope, a flexible tube outfitted with a small video camera and a light.
But concern around pre-colonoscopy bowel cleaning, which can be uncomfortable and unpleasant, may contribute to low screening rates. Your bowel needs to be completely empty during colonoscopy to give your doctor a clear view of your intestinal wall; preparing for the test involves drinking a liquid that triggers bowel-clearing diarrhea.
CRC screening tests: Other options
So, while colonoscopy remains the gold standard, the best test is the one that gets done or gets the process started. A recent meta-analysis found that fecal blood tests, which are available by prescription and can be done at home, are associated with increased screening rates. (Patients still need a colonoscopy if there is an abnormal result, to diagnose cancer or remove polyps to prevent cancer.)
In 2016, the United States Preventive Services Task Force updated its CRC screening recommendations to state that patients and physicians can choose among available screening tests.
Currently, three types of at-home CRC screening tests are approved by the Food and Drug Administration (FDA):
- Guaiac FOBT (gFOBT) uses a chemical to detect a component of hemoglobin, a blood protein in the stool.
- Fecal immunochemical test (FIT or iFOBT) uses antibodies to detect hemoglobin shed by polyps or colorectal cancer.
- Multitarget stool DNA test (FIT-DNA) detects trace amounts of blood and DNA from cancer cells in the stool.
For all of these tests, you collect a stool sample at home using a kit, then mail the sample to a doctor or to a laboratory for testing. None require the bowel-clearing prep required for colonoscopy. Amazon sells screening tests: FOBT for $10 and FIT for $25. These are available without a prescription but are not as well studied or standardized as those available through your physician.
Pros and cons of at-home CRC screening tests
A review published in JAMA concludes that all three home tests may be an efficient first-step for low-risk patients. However, all the kits, as well as colonoscopy, can miss polyps, which can and should be removed at the time of the colonoscopy.
The FIT screening test has been in use for about 10 years. It should be repeated annually in case the cancer or polyp isn’t bleeding at the time of the test. (Colonoscopy is recommended once every 10 years for low-risk patients.) The FIT test detects cancer with 79% accuracy, with about 5% false positive results (suggesting cancer where none exists), which warrant a colonoscopy for further testing.
Studies have shown that the multitarget stool DNA test (Cologuard is currently the only FDA-approved brand) detects cancer with 92% accuracy. However, 14% of tests deliver a false positive result, which is higher than the FIT test. Health experts recommend repeating the test every one or three years.
For years we have used the gFOBT to detect microscopic amounts of blood in the stool that is not visible to the naked eye. It is less accurate than either the FIT or the DNA stool test, identifying only 20% to 50% of cancers. This test has a limited role today.
An additional barrier to CRC screening is the out-of-pocket cost to patients. The Affordable Care Act mandated that insurance plans cover CRC screening tests, including colonoscopy, in full, with no out-of-pocket cost to patients. However, coverage does not apply to colonoscopies that convert from screening to diagnostic when a polyp is detected and removed during the procedure. And coverage does not apply to diagnostic colonoscopies after a positive CRC FIT or DNA screening test result.
This coverage failure means that patients may have to pay thousands of dollars to complete recommended CRC testing.
How can you decide which CRC screening test is right for you?
Ask your doctor and have a frank discussion about your risks and concerns. Most people find colonoscopy less miserable than they anticipate, and it is still the best option overall. Higher-risk people really do need a colonoscopy, usually until age 80. For others, get tested or get the screening process started, and the only wrong answer is ignoring the possibility of colon cancer.