There is no universally agreed answer. My own view is that if:
The blood is “cut finger” bright red, AND
Is only ever seen on the toilet paper, OR
Drips or sprays on to the bowel wall during defecation, then the lesion should be within 60cm of the anus and should be able to be seen at flexible sigmoidoscopy.
HOWEVER, if the patient:
Is unsure of the bleeding details or is a poor historian, visually impaired “didn’t look” etc.
Has other risk factors (e.g. family history, previous carcinoma of the colon, previous colonic polyps or inflammatory bowel disease).
Is anxious about the possibility of carcinoma;
Then full colonoscopy is to be preferred. NB visualization of bleeding from a haemorrhoid does NOT prove that this is the source of PR bleeding . Digital examination and proctoscopy can precipitate haemorrhoidal bleeding.