Fecal occult blood testing in colorectal cancer screening programs

Abstract

Colorectal carcinoma (CRC) is the third most common cancer worldwide and ranks second as a cause of cancer mortality. CRC screening is carried out in many countries for detection early-stage CRC and its prevention by removing precancerous lesions, and includes fecal occult blood testing and colonoscopy. Different countries use their own approach to screening, including methods of detection of fecal occult blood. The strategy for fecal occult blood testing is based on the fact that already in the early stages the tumor can bleed, and small traces of blood in the stool are detected before the onset of clinical symptoms of the disease. Different countries use their own approach to the CRC screening, including methods for fecal occult blood testing. Chemical and immunochemical methods are used to determine occult blood in the feces. The chemical method is based on the detection of heme peroxidase activity. The immunochemical method detects human globin using specific antibodies. The immunochemical method can be qualitative and quantitative. The sensitivity of a quantitative immunochemical test depends on the selected threshold and the stage of CRC. The lower the threshold value, the higher the sensitivity, but the lower the specificity due to false positive results. CRC screening programs use different thresholds for quantitative immunochemical testing in different countries, which is caused by the availability of colonoscopy in a positive test result, as well as the rate of CRC in this population. To increase the sensitivity of the immunochemical test, some programs suggest using it in combination with other methods: detection of DNA in stool, examination of other proteins in feces (transferrin, haptoglobin). This review presents the methods used in the world for fecal occult blood testing, their advantages and limitations; recommendations for reporting the results of a quantitative immunochemical test; thresholds recommended in screening programs in different countries for quantitative immunochemical tests. The results of pilot screening for fecal occult blood testing in some regions of the Russian Federation are also presented.