Is a positive stool test (either a Fecal Occult Blood Test (FOBT), or the more recent CoLogic test) a cause for serious concern?
A positive Fecal Occult Blood Test (FOBT) is very common, and in the vast majority of cases, nothing to worry about. This does not mean, however, that it doesn’t require proper follow-up investigation.
The FOBT (stool test) is used as a screening test for colon cancer because one of the early signs of colon cancer is rectal bleeding. The FOBT test detects a very small amounts of blood in the stools by a chemical test -- in essence detecting bleeding long before you can see it with your eyes. So it picks up very, very small amounts of rectal bleeding .
The problem with the test is that blood from anywhere will cause the test to be positive (such as bleeding gums when you brush or floss your teeth, if you swallow that saliva, nosebleeds, if you swallow any of the blood, or even a rare steak, in which case it’s the blood from the cow that can turn the test positive). Even molecules that look and react similarly to blood will be detected ( medications, certain foods). Still, the FOBT is a simple, inexpensive way to detect colon cancer. If your test was positive, you probably don’t have colon cancer; in fact studies have reported that the percentage of patients who actually have cancer when their FOBT is positive (“ the positive predictive value of FOBT”) varies widely, as low as 2.5%, and probably no higher than 10%. So your chances of having a cancer are low, but wouldn’t you want to investigate the possibility that you had an even 1 in 40 chance of a potentially fatal illness? This is why we say on the one hand don’t worry because the odds are between 10-1 and 40-1 that you are perfectly healthy
but on the other hand these positive results MUST be followed up with a colonoscopy.
Usually we recommend only a colonoscopy. In some patients who have a high likelihood that their intestinal bleeding might have been from acid reflux or stomach ulcer, a gastroscopy is also recommended. Both tests can be performed at the same time. You can find out about colonoscopy and gastroscopy on this website, including how to prepare for them. Your procedure can usually be completed within a few weeks of referral, (we aim for a two-three-week waiting list only) and you will have your own copy of the results burned onto a CD that you can take home with you. You will have closure over the issue on the day of your procedure.
Useful resources about fecal occult blood testing are found at this website, and there is a dedicated slideshow available for viewing or download on our podcast page. You can also view a slideshows about colonoscopy and gastroscopy on the podcast webpage.
The CoLogic test is a newer blood test that is being used for colon cancer screening. Based on current evidence, it is no longer a recommended colon cancer screening test.
Overall, you should not be worried if your only symptom is a random positive test. The odds are highly against you having any serious problems. But that needs to be established beyond any reasonable doubt, with colonoscopy.
Lastly, it is certainly possible you can have your consultation and your procedure done on the same day. We ask that you visit our same day consultation page, and it is also possible to request appointments, and book your procedure entirely online. If you would rather deal with real people, please call our Office Manager, Mary, at the phone numbers above. We are happy to communicate with patients by e-mail, also. This can include confirmation and reminders about appointments, and other questions.
Back to FAQ