[[Evaluation of various methods of studying fecal occult blood]

Occult blood testing for detection of asymptomatic colorectal cancer is an old concept. The authors review the literature about the screening value of current tests. Among the chemical tests, Hemoccult is the most popular and the best studied. Sensitivity and specificity are moderate. False negative reactions are due either to the test itself (high level of sensitivity, loss of reactivity) or to the tumour (intermittent or insufficient bleeding, localization etc...). False positive reactions are due to the interference of a high peroxidase diet. The Hemoccult test is nevertheless interesting because it is simple, cheap and well accepted. Detected cancers tend to be at a relatively early stage: 60 to 80% of Dukes A or B. New methods--Hemoquant and immunochemical methods--are being developed. Their high degree of sensitivity and specificity for human hemoglobin makes them too complex and too costly. Whatever the efficacity of a test to detect occult blood may be, we must know whether the screening of an asymptomatic population could decrease the mortality rate of colorectal cancer, before using it on a large scale. Only long-term controlled trials can give us an answer in the future.