[Two-phase test of fecal occult blood screening for colorectal cancer]

The detection of colorectal cancer in an early curable stage has become the focus of considerable interest recently. A two-phase test using both guaiac test and Hemolex latex immuno-agglutination test was applied for fecal occult blood screening of colorectal cancer. A total of 4,725 veterans aging 60 to 69 years were registered, and 2,176 persons (average age 66 years) completed the test giving a compliance rate of 46%. The positive rates of both tests were accounted 20.5% and 6.7% respectively. Five hundred and forty five persons had positive reaction for at least one of the tests. Of these, 90 had a follow up diagnosis with colonoscopy or combined with barium enema. Three rectal adenocarcinomas were detected, of which only one was positive by guaiac test, but two by Hemolex test. A rectal carcinoid was found by rectodigital examination. It was negative by both tests. Nineteen cases were detected to have one or more polyps in colon or rectum, of which only 6 were positive by guaiac test, but 18 by Hemolex test. Hemolex test using antibody against human hemoglobin is based on latex agglutination reaction. It is more sensitive and specific than guaiac test. Moreover, no dietary restriction is required. In the view point of cost-effectiveness, mass screening for colorectal cancer in general public is not recommended, but hospital-based screening for high risk group is still worthwhile to study.