Colorectal cancer (CRC) is one of the most common cancer worldwide, and cause a huge number of cancer-associated mortality. CRC screening has been shown to be effective in reducing the incidence of, and mortality from, CRC. There are several recommended screening options for screening population of CRC, including colonoscopy and fecal occult blood testing (FOBT) .Colonoscopy has higher sensitivity and specificity than FOBT for detecting advanced colorectal neoplasia but also has several disadvantages, including higher cost and poorer compliance. Therefore, many patients prefer FOBT to colonoscopy. FOBT includes guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT). FIT includes quantitative FIT (qFIT) and qualitative FIT. qFIT can provide a value of concentration of hemoglobin in stool and are increasingly recommended for CRC. In China, the most common use FOBT is qualitative FIT and the comparison of quantitative and qualitative FIT is lack in screening population of CRC in Chinese. To add to the evidence on FIT performance characteristics for detection of CRC, the investigators design this research to compare qFIT with other 3 qualitative FOBT（two of them are colloidal gold qualitative FITs and one of them is chemical and immunologic combined detection）in medium and high risk screening population.
