Predictive value of rectal bleeding in screening for rectal and sigmoid polyps.

Overt rectal bleeding is a common symptom of colorectal cancer and polyps but also occurs in apparently healthy people. It is not known how often this represents bleeding from an undiagnosed rectal or sigmoid polyp or cancer. Three hundred and nineteen apparently healthy men aged over 50, selected by random sampling, were interviewed and underwent flexible sigmoidoscopy to at least 30 cm. Polyps of 10 mm or more in diameter were diagnosed in 12, one of whom also had an adenocarcinoma. Rectal bleeding during the previous six months was reported by 48, four of whom were found to have polyps; seven polyps and one cancer were diagnosed among the 271 who reported no rectal bleeding. Rectal bleeding had a specificity of 86%, a sensitivity of 33%, and a positive predictive value of 8% for rectal or sigmoid polyps or cancer. Restricting the analysis to those subjects who regularly inspected their stools did not improve the predictive value. Sigmoidoscopy in apparently healthy subjects with rectal bleeding will not result in the diagnosis of appreciable numbers of rectal and sigmoid polyps or cancers.