Blood test is not able to detect cancer cells, and blood test is mainly to check tumor markers, which are manifested due to secretion of cancer cells, so the test is to check tumor markers. If the tumor marker of blood test is high, further related examination should be carried out, for example, gastroscopy and colonoscopy can be carried out when the tumor marker of gastrointestinal tract is high. If the tumor markers of the lungs are high, chest CT examination can be performed, and then further treatment can be performed according to the results of the examination.