Cologuard Test Is Worth Risk of a False Positive

DEAR DR. ROACH: I am a 77-year-old man in good health. At my recent annual physical exam, my physician ordered a Cologuard kit to be sent to me to screen for colorectal disease. I have never had symptoms of disease or problems with any part of my gastrointestinal tract. I had two colonoscopies at different times several years ago, with negative results. When I got the kit, I read that the Cologuard test could result in false positives, with an increased risk of false positives for persons over age 75. A positive test result requires a follow-up colonoscopy, which is also riskier for elderly patients. Since I am in good health with no symptoms of any disease, I decided I did not want to risk a false positive result from the test, which would require a follow-up colonoscopy. Did I make the right decision? -- E.G.

ANSWER: Cologuard is a brand of test that looks at DNA in stool for evidence of cancer. Certain DNA mutations are highly suggestive of cancer. In addition, Cologuard does an immunochemical test looking for blood. Because it combines these two techniques, Cologuard is more sensitive than only a test looking for blood. Compared with colonoscopy, Cologuard is about 92% sensitive in finding cancers, meaning it will miss about 8%. With improved sensitivity comes a lack of specificity, which means you could have a false positive result. The Cologuard can say that you have an abnormality when a colonoscopy would indicate normal. For 45% of people with a positive Cologuard test, no abnormalities will be found upon colonoscopy. You are right that false positives are more prevalent in older individuals.

There are two reasons that I think the Cologuard is still a reasonable choice, although it isn’t as good as colonoscopy. The first is that I continue to recommend a screening test for healthy 77-year-old men, and although colonoscopy is my first choice, a normal Cologuard test prevents a need for colonoscopy, and a false positive would lead to the same colonoscopy you would have gotten anyway (although there probably is more anxiety after a false positive test). The second is that a person with an abnormal Cologuard and a normal colonoscopy may be at risk for an abnormality that wasn’t found on colonoscopy. A study looking at people in this category found a 25% risk of abnormality on follow-up colonoscopy, if the Cologuard was abnormal again one to two years later.

***

DEAR DR. ROACH: I am 35 years old. I have experienced fluttering in my chest for most of my adult life. It’s been a once in a while kind of thing, but for the past month, I keep getting it every day. I have had a lot of EKGs, but my doctor seems to think everything is normal. Please help me, because it’s messing up my work and other aspects of my life. -- S.Q.

ANSWER: Most of the time, fluttering in the chest is not something you need to worry about. Most people will have occasional episodes of this, and a few people have a greater number but are found to be normal after extensive evaluation.

A cardiologist might recommend a 24- to 48-hour heart monitor. If you have symptoms every day, this would be likely to catch your heart rhythm during an event. Devices that record for longer amounts of time are also available, and there are consumer devices that allow you to record an EKG yourself.

Dr. Roach regrets that he is unable to answer individual questions, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@ med.cornell.edu.