Carcinoembryonic Antigen (CEA) is a protein that circulates in the bloodstream and is measured through a simple blood test. It is one of the most common tumor markers used to monitor certain cancers, most notably colorectal cancer. While a high number on a CEA level chart can be concerning, the figure itself is not a diagnosis. Understanding the meaning of these numbers requires context, looking at both the biology of the protein and the clinical situation of the patient.
The Biological Role of Carcinoembryonic Antigen
Carcinoembryonic antigen is a glycoprotein, a protein with attached sugar molecules, whose primary function relates to cell adhesion. This protein is produced in large quantities during the second trimester of fetal development, particularly in the gastrointestinal tract, supporting the rapid growth and differentiation of the gut lining. After birth, the gene that produces CEA is typically switched off, causing the protein to largely disappear from the bloodstream of healthy adults.
In an adult, the presence of elevated CEA levels suggests a resurgence of this protein production, which is often a marker of rapid cell turnover or inflammation. CEA belongs to the immunoglobulin family, specifically the CEACAMs (CEA-related cell adhesion molecules). Elevated levels are not specific to cancer, but malignant cells, such as those in colorectal tumors, can reactivate the production of this developmental protein.
Interpreting the CEA Level Chart
The interpretation of a CEA number depends heavily on established reference ranges. For healthy, non-smoking adults, a normal CEA level is generally considered to be below 2.5 nanograms per milliliter (ng/mL). Because the protein can be elevated by chronic irritation, a level up to 5.0 ng/mL is often considered acceptable for individuals who smoke cigarettes.
A level slightly elevated above the normal range, typically falling between 5.0 ng/mL and 10 ng/mL, requires further investigation. This range may suggest a localized tumor, but it is also commonly seen in various non-cancerous conditions. Levels significantly above 10 ng/mL, and especially those exceeding 20 ng/mL, are highly suggestive of cancer and often correlate with metastatic or widespread disease. A single high number is never used to screen for cancer in the general population because the test lacks the necessary sensitivity and specificity.
Benign Causes of Elevated CEA Results
An elevated CEA level can result from many non-malignant conditions that cause a temporary or sustained rise. Heavy smoking is the most common benign cause, with chronic irritation to the respiratory and digestive tracts leading to increased CEA production.
A variety of inflammatory and chronic diseases of the digestive system can also cause CEA levels to rise moderately. These include inflammatory bowel diseases (IBD), such as ulcerative colitis and Crohn’s disease, as well as diverticulitis. Conditions affecting the liver, such as hepatitis or cirrhosis, and inflammation of the pancreas (pancreatitis) can also lead to modest elevations. In these non-cancerous scenarios, CEA levels usually stay below the 10 ng/mL threshold.
Using CEA to Track Cancer Progression
CEA is used to monitor patients diagnosed with a CEA-producing cancer, such as colorectal, lung, or breast cancer. Before treatment begins, a baseline CEA level is established to serve as a point of comparison for future results. Serial testing is then performed at regular intervals, often every three to six months, to track the disease over time.
A steadily increasing trend in CEA levels over several months is the most concerning result, often indicating cancer recurrence or progression even before symptoms appear. Conversely, a sharp drop in the CEA level following surgery or chemotherapy is a positive sign, suggesting that the treatment has been effective at reducing the tumor burden. If the CEA level was elevated before surgery but fails to return to the normal range afterward, it may signal that the cancer was not completely removed or that residual microscopic disease remains. Interpreting these results also requires caution, as a temporary rise, or “CEA flare,” can sometimes occur shortly after starting chemotherapy, which does not necessarily indicate treatment failure.