CA199 is a marker for digestive tract tumors, including pancreatic cancer, colon and rectal cancer. CA199 is a tumor cell-associated antigen and is by far the most sensitive marker for detecting pancreatic cancer. It has a critical value of 37Ku/L. When CA199 consistently exceeds this value and is at a high level, a malignant tumor is considered likely. Of course, for the diagnosis of the tumor, we also need imaging data and pathological diagnosis as an auxiliary judgment basis. When CA199 is not always at a high level, but low concentration increase or transient increase, it suggests that there may be chronic pancreatitis, cholelithiasis, cholecystitis, cirrhosis of the liver, diabetes and other diseases, and other diagnostic aids are needed to confirm the diagnosis of specific diseases.