Can a fit test detect visible blood in stool or just non visible blood? i have on and off blood in stool, intermittent constipation & diarrhea, and today lots of thick mucus, wil fit be positive because of the visible blood and give a false reading?

A FIT test detects blood in stool.whether it's hidden or obvious. It would be unnecessary if you're passing obvious blood rectally. It doesn't diagnose cancer. You should be evaluated by a gastroenterologist to determine the cause of your rectal blood. In my opinion, inflammatory bowel disease or proctitis vs irritable bowel syndrome coupled with hemorrhoids is the differential diagnosis here.