Faecal occult blood testing in the detection of colorectal cancer.

5012 asymptomatic patients over the age of 40 years were asked by their general practitioners to perform a Hemoccult faecal blood test over 3 days. 3422 patients on a normal diet completed the test (a compliance rate of 67 per cent). Ninety-nine patients (3 per cent) had a positive result. Those patients with a positive result then underwent a second Hemoccult test over 6 days on a restricted diet. Thirty-two patients had a positive result on repeat testing (1 per cent). Only those patients who were positive on the second testing were fully investigated (including double contrast barium enema and colonoscopy). Twenty-seven patients on investigation were found to have neoplastic disease (84 per cent). Twelve had invasive carcinomas (nine Dukes' A, two Dukes' B, one Dukes' C) and thirty-seven adenomas were identified and removed at colonoscopy (barium enema missed three carcinomas--all dukes' A and only identified sixteen of the thirty-seven adenomas, 43 per cent). Those patients found to be negative after the second Hemoccult test are being followed up.