Screening of colorectal tumours using an improved faecal occult blood test. Quantitative aspects.

A recently developed double test for detecting faecal occult blood (a sensitive guaiac test combined with a quantitative immunological human haemoglobin test), was adapted to population screening. The study involved an unselected population of 10,343, aged 49-74 years. There was 66.5% participation. 174 colonoscopies were done, yielding seven adenocarcinomas, 44 adenomas and four hyperplastic polyps. By eliminating benign anal tract bleeding, the number of endoscopies decreased from 340 to 174. Most tumours showed an absorbance over 0.80, and it is suggested that by setting the lower limit of positivity at the 0.80 absorbance level, the number of clinical examinations could fall to about 1%, without substantially missing tumours.