Mercy's Dr. Jeffery Nelson Discusses The Efficacy of Home Colon Cancer Screening Tests

October 09, 2020


Experienced colon and rectal surgeon Dr. Jeffery Nelson, Surgical Director of Mercy's Center for Inflammatory Bowel and Colorectal Diseases, recently responded to a query from VeryWell Health concerning the efficacy of home colon cancer screening tests. Here are his insights…

The three tests that can be done at home are the fecal occult blood test (FOBT), fecal immunochemical test (FIT), and the multi-target  stool DNA test (i.e. Cologard). FOBT has been in use for decades and tests for blood using a small sample from the patient. It only detects colon cancer about 30-50% of the time and is really only useful in conjunction with flexible sigmoidoscopy. FOBT plus flex sig should be repeated every 5 years. The problem is that it is very non-specific and there many things that can cause false positive results – Vitamin C, red meat, broccoli, horseradish, etc. It also is not specific for bleeding only in the colon – it could be from anywhere in the GI tract.

FIT testing has largely replaced FOBT, because it is much more sensitive and specific for bleeding sources in the colon. It tests for hemoglobin only from a lower GI source. It has about a 5% false positive rate, however, necessitating a trip for colonoscopy. It should be repeated every year, but only requires a small stool sample similar to FOBT.

Cologard tests for DNA from colon cancers specifically. It is very sensitive, but this results in about a 14% false positive rate, and thus needs to be followed up with full colonoscopy to rule out a colon cancer. This can lead to high anxiety in some patients, and they should be counseled on this issue with Cologard before doing it. Cologard should be repeated every one to three years, but the actual necessary interval has not been established yet, due to the newness of the test. It also requires submission of an entire bowel movement to the lab.

All these tests are for patients at AVERAGE risk of colon cancer. This very important point gets lost (or completely ignored) in the advertisements. If a patient has any risk factors for colorectal cancer, then colonoscopy really is the only appropriate screening and surveillance modality they should get.

Jeffery Nelson, M.D. - The Center for Inflammatory Bowel & Colorectal Diseases, The Institute for Digestive Health and Liver Disease at Mercy

About Mercy

Founded in 1874 in Downtown Baltimore by the Sisters of Mercy, Mercy Medical Center is a 183-licensed bed, acute care, university-affiliated teaching hospital. Mercy has been recognized as a high-performing Maryland hospital (U.S. News & World Report); has achieved an overall 5-Star quality, safety, and patient experience rating (Centers for Medicare and Medicaid Services); is A-rated for Hospital Safety (Leapfrog Hospital Safety Grade); and is certified by the American Nurses Credentialing Center as a Magnet™ hospital. Mercy Health Services is a not-for-profit health system and the parent company of Mercy Medical Center and Mercy Personal Physicians.

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