Improved screening for colorectal cancer by immunological detection of occult blood.

A radial immunodiffusion technique for detecting faecal haemoglobin and the Hemoccult II kit used with and without rehydration of the faecal sample were compared in a screening programme for bowel cancer, in which 1328 subjects took part. A positive result was obtained in 170 (13%) subjects. Nineteen of the 153 subjects investigated were found to have colorectal carcinomas and 52 had polyps (40 with adenomas). Radial immunodiffusion and Hemoccult II with and without rehydration detected bleeding in, respectively, all 19, 15, and 11 subjects with colorectal carcinoma. Hemoccult II with and without rehydration detected only seven and six, respectively, of 11 Duke's stage A carcinomas, whereas all 11 were detected with the immunological test. Hemoccult II with and without rehydration and radial immunodiffusion detected bleeding from adenomas in, respectively, 22, 14, and 34 of the 40 subjects. False positive results occurred in 55 out of 1302 subjects by Hemoccult II with rehydration, in 28 out of 1304 by Hemoccult II without rehydration, and in 50 out of 1304 by the immunological technique; true positive results were defined as bleeding from carcinomas and adenomas. Immunological detection of occult blood in faecal samples seems to show more adenomas and carcinomas (particularly early lesions) than the Hemoccult II kit and has a rate of false positive results that is acceptably low.