Hereditary polyposis coli I: the diagnostic value of colonoscopy, barium enema, and fecal occult blood.

In families with one of the Mendelian hereditary polyposes, one can predict the proportion of patients at risk and thus obtain a denominator against which colonoscopy, barium enema, and fecal occult blood can be validated. Colonoscopy is more sensitive than barium enema. There were 42 positive colonoscopies, 12 positive barium enemas, both being positive in 10 of these. There were 141 negative enemas, 133 negative colonscopies, and 118 negative for both. Occult blood was positive in 30% of patients with polyposis, five to seven times more frequently than in those without evident polyposis. Colonoscopy detected polyposis in 30% of the progeny of affected people. The shortfall, compared with the 50% expected under the Mendelian hypothesis, is readily explained by removal of affected cases from the study by surgery or death from cancer.