What is the meaning of CEA test?

Maybe marks tumor. Cea is a protein that can be made by some malignant tumor cells (cancer-ca). Some benign diseases can increase cea levels. High cea doesn't make a diagnosis. Helpful for follow up. If ca diagnosed, cea checked. If elevated, follow after treatment. So if cea high before surgery, cea should fall after, and with chemo/rt. Cea rises can be with recurrence or metastatic spread. Lower is better.
Smokers & CEA. Agree with other drs. Some smokers may have slightly high cea with no other apparent reason. So there are some false positives tests too. That is why cancer markers cannot be used alone for screening purposes.