Elevated carcinoembryonic antigen is a common indicator in medical examinations. Elevated carcinoembryonic antigen is mainly seen in common tumors of the gastrointestinal tract, namely gastric, colorectal and pancreatic cancers, and is also used in lung adenocarcinoma to monitor the efficacy of lung adenocarcinoma. However, when carcinoembryonic antigen is elevated, the first thing to look at is the value of the elevation. A normal carcinoembryonic antigen is within 0-10 μg/L. A mild elevation such as 0-20 μg/L requires dynamic observation, but if the carcinoembryonic antigen is greater than 100 μg/L, it requires high vigilance and CT scan with enhancement of the whole abdomen and endoscopy of the whole gastrointestinal tract to exclude the possibility of gastrointestinal tumor. CT plain scan of the lungs can also be done, especially for those middle-aged men who are long-term smokers.