Carcinoembryonic antigen, also known as CEA, is a commonly used tumor marker with clinical reference values ranging from 0-4ng/ml, some testing institutions may have reference values below 6ng/ml and some below 5.9ng/ml. The normal value of carcinoembryonic antigen may vary among different testing institutions and different testing methods, but as long as it is not much higher than the normal value, it is not a big problem. Carcinoembryonic antigen may be more elevated in colon malignancies and lung malignancies, such as more than 50ng/ml or 100ng/ml, or even more. If this index is slightly elevated, for example, >4ng/ml or >10ng/ml, a mild elevation does not mean anything, but it should be combined with the presence of colitis and pneumonia, and it is better to do chest CT and colonoscopy to assist the diagnosis.