Occurrence and clinical significance of overt blood loss per rectum in the general population and in medical practice.

While the occurrence of blood loss per rectum in general practice is common and usually not serious, it may be the first symptom of a colorectal malignant disorder. To determine the occurrence and clinical significance of overt blood loss per rectum a Medline literature search was undertaken. The incidence of this symptom in the general population was reported to be approximately 20 per 100 people per year, the 'consultation incidence' in general practice approximately six per 1000 and the incidence of referral to a medical specialist was estimated to be about seven per 10,000 per year. The clinical significance of the symptom varied within different populations: the predictive value of overt rectal blood loss for colorectal malignancy was estimated to be less than one in 1000 in the general population, approximately two in 100 in general practice and up to 36 in 100 in referred patients. How the manifestation of the bleeding (and other signs and symptoms) contributes to the selection of patients at each of these stages, leading to increasing prior probabilities, is unknown.