It's a low specificity test. If you get a false positive you'll be getting a colonoscopy anyway, and (less of a risk, but still worth considering) if you get a

It's a low specificity test. If you get a false positive you'll be getting a colonoscopy anyway, and (less of a risk, but still worth considering) if you get a false negative it's a bit of a problem. That's how my gastro explained it, and a bit of my own internet research supported.