Immunochemical detection of fecal occult blood--the fecal smear punch-disc test: a new non-invasive screening test for colorectal cancer.

An immunochemical test for fecal occult blood was developed for use in colon cancer screening. The test employs high titer monospecific antisera to intact human hemoglobin in a radial immunodiffusion assay. Patient smears on specially treated filter paper allow screening procedures similar to those using Hemoccult slides. Minimum detectible hemoglobin was 0.3 mg/gm stool, and no cross reactivity with dietary constituents, drugs, or chemicals occurred. The accession of 150 consecutive cases of colon-rectal carcinoma was accomplished from three community hospitals. In each instance, at least one preoperative fecal specimen was obtained for companion smear testing with immunochemical punch-disc and commercial Hemoccult slides. Twenty-nine percent of the cases were found not to be bleeding by either test. Occult bleeding was detected by Hemoccult in 40% of the cases, and occult bleeding was detected by immunochemical testing in 65% of the cases. A surprising discovery was that rectal lesions had a much lower rate of of positiuity with both tests (Hemoccult-29%, Immunochemical-50%) than other locations. These results suggest that immunochemical screening for occult blood loss will provide a higher rate of detection of colon cancer.