A CEA test result of 20 nanograms per milliliter or higher is a very high level, according to Healthline. A level this high not only strongly suggests the presence of cancer, it can also mean that the cancer has metastasized, or spread to other parts of the body.
CEA levels above 3 nanograms per milliliter are abnormal and could indicate the presence of cancer, though it does not directly mean that the person has cancer, Healthline explains. Otherwise healthy smokers sometimes show higher levels of CEA, but never above 5 nanograms per milliliter. Doctors often administer the CEA test to patients who have already been diagnosed with cancer to determine the effectiveness of treatments, and a very high level usually indicates that treatments are not working.