The normal range of carcinoembryonic antigen is 0~5.0ng/ml, carcinoembryonic antigen 15.5ng/ml is considered as high carcinoembryonic antigen, whether it is serious or not depends on the cause of the elevated carcinoembryonic antigen. Carcinoembryonic antigen is a broad-spectrum tumor marker, and there are many causes of elevated carcinoembryonic antigen, including smoking, benign diseases such as gastritis, gastric ulcer, gastric polyp and tuberculosis, and malignant diseases such as gastric cancer, intestinal cancer, lung cancer and breast cancer. Carcinoembryonic antigen increase due to gastritis, gastric ulcer and smoking is not serious; carcinoembryonic antigen increase due to malignant tumor is more serious. Elevated carcinoembryonic antigen due to benign diseases is not serious, and the value of carcinoembryonic antigen may drop back to normal after treatment of the cause of the disease. On the other hand, elevated carcinoembryonic antigen due to malignant tumors should be taken seriously, as malignant diseases can seriously affect the life expectancy of the patient and require prompt treatment. Therefore, patients with carcinoembryonic antigen 15.5ng/ml should go to the hospital in time, complete the examination, and give targeted treatment after clarifying the cause of the disease.