Very good question. I would say no test in medicine is absolutely 100% in diagnostic rates. There is always a small missed rate, so a colonoscopy will likely detect around 99% or so of polyps.
Sometimes there are reasons why polyps may be missed during the colonoscopy because the intestine, the curvature of one’s intestine, varies from person to person. Sometimes there is an acute angle where the view of the scope to see or examine is not full or the entire circumference of the intestine you would like to see.
So, it is possible to miss some or there might be a blind spot where the doctor doing the colonoscopy can not see and sometimes say if the bowel preparation is not clean, prior to going for a colonoscopy it is routine to consume something called bowel preparation, which means you are given something to clear the bowel and flush your system clean.
So if the bowel preparation is not so good, meaning there is still a lot of residues, you can’t see everything. So these are some reasons why the polyps can be missed, but these are not that common.
