Carcinoembryonic antigen was 6.6ng/ml five months ago and now it is 6.3ng/ml, whether it is serious or not depends mainly on the cause of the elevation. The normal range of carcinoembryonic antigen is <5.0ng/ml, so 6.6ng/ml and 6.3ng/ml are both on the high side. Carcinoembryonic antigen is a commonly used marker for diagnosis of tumors in the clinic, which mainly includes malignant tumors such as lung cancer, ovarian cancer, breast cancer, etc., so it is possible that it is more than 5.0ng/ml but it can't be used as a specific indicator for diagnosis of a certain kind of malignant tumors, and it needs to be combined with CEA indicator for auxiliary diagnosis. It is also necessary to combine with CEA index for auxiliary diagnosis. Carcinoembryonic antigen may be elevated due to smoking, 20% of smokers have carcinoembryonic antigen over 5.0ng/ml, and also due to benign diseases such as cirrhosis of the liver, gastrointestinal polyps, rectal polyps, etc. Carcinoembryonic antigen may reach 6.3ng/ml. It is recommended to go to the hospital for examination to find out the cause of the disease and treat the symptoms.