Immunological detection of occult blood in bowel cancer patients.

The ability of a highly sensitive gel immunodiffusion technique to detect faecal occult blood in control subjects and in patients with colorectal carcinoma, was compared to that of Hemoccult II. In 1,200 samples from 200 control subjects, 3.3% were positive by the immunological technique, 5.0% by Hemoccult II with rehydration and 2.3% without rehydration, representing 7.5%, 10.5% and 5.0% of subjects, respectively. A total of 2 carcinomas and 6 polyps were detected in the 27 positive subjects. False positive results were 4.5% for the immunological technique, 7.5% and 3.0% for Hemoccult II with and without rehydration. All 40 patients with colorectal carcinoma had at least 1 in 6 samples positive on immunological testing and 79.2% of all samples were positive. With Hemoccult II, without rehydration, 52.1% of samples and 71.8% of patients were positive. These values increased to 66.3% and 87.5% with rehydration. It is concluded that: (i) The proportion of false positive results on immunological testing is low enough to allow screening of populations for colorectal carcinoma using this technique. (ii) Using 6 faecal samples, this technique detected bleeding from 100% of colorectal carcinomas in the study.