Occult blood testing for early detection of colorectal cancer: diagnostic outcomes.

Three thousand five hundred and fifty-four asymptomatic persons from 32 family practices returned hemoccult II tests for colorectal cancer; 2.2% of these returned tests were positive. The diagnoses for the 47 persons with positive tests which were done while on meat restriction included six cancers (1.7/1000) and five polyps (1.4/1000); 18 were diagnosed with other known sources, and 18 were undiagnosed. All polyps and four of six cancers were diagnosed by combined barium enema with sigmoidoscopy or by colonoscopy. Five of six cancers were diagnosed at early stages. Meat restriction, the method of returning the test for analysis, the number of holes completed in the test, and the delay time from completing the test to analysis did not influence the likelihood of a positive test.