What is a CEA Blood Test?
A CEA (carcinoembryonic antigen) blood test measures the level of a glycoprotein in your blood that can be elevated in various cancers—particularly colorectal cancer—as well as in benign conditions and even in heavy smokers.
What CEA Actually Measures
CEA is a glycoprotein (a protein with sugar molecules attached) that is normally produced by various tissues in the body 1, 2. The test uses radioimmunoassay or other immunologic techniques to measure the amount of this protein circulating in your blood 3. Normal CEA levels are typically defined as less than 2.5-5.0 ng/mL, though the exact cutoff varies between laboratories 4, 2.
Clinical Uses of CEA Testing
What CEA Should NOT Be Used For:
- Screening for cancer in the general population - CEA is explicitly not recommended for mass screening because its sensitivity is very low for early-stage disease, leading to too many false-positive and false-negative results 4, 1
- Diagnosing cancer by itself - The test cannot provide enough diagnostic certainty to confirm or rule out suspected cancer on its own 1
What CEA IS Useful For:
In Colorectal Cancer Management 4:
- Preoperative staging: May be ordered before surgery to help with staging and treatment planning; elevated levels (≥5 mg/mL) correlate with poorer prognosis
- Postoperative surveillance: Should be measured every 3 months for at least 3 years in stage II or III colorectal cancer patients who are candidates for further treatment
- Monitoring treatment response: The marker of choice for monitoring metastatic colorectal cancer during systemic therapy, measured every 1-3 months during active treatment
- Detecting recurrence: An elevated CEA after surgery, when confirmed by retesting, warrants further evaluation for metastatic disease
CEA can be elevated in multiple cancer types beyond colorectal cancer, including:
- Pancreatic cancer (often shows highest elevations)
- Lung cancer
- Breast cancer
- Medullary thyroid carcinoma 7
Important Caveats
Benign Conditions Can Elevate CEA 2, 5:
- Inflammatory bowel disease
- Pancreatitis
- Lung inflammation
- Liver disease
- Uremia
- Normal aging (levels increase in people over 65)
Smoking significantly affects CEA levels - heavy cigarette smokers can have elevated CEA without any cancer present 2, 3.
Chemotherapy can cause false elevations - CEA levels may spuriously rise during the first 4-6 weeks of new therapy, particularly with oxaliplatin 4. Therefore, waiting until chemotherapy is finished before initiating CEA surveillance is advised 4.
Laboratory variation exists - measured CEA levels may differ between laboratories and countries, so consistency in testing location is important 4.
The Bottom Line
CEA is primarily a monitoring tool rather than a diagnostic test. Its greatest clinical value lies in tracking disease progression or recurrence in patients with known colorectal cancer, where rising levels can detect metastatic disease before symptoms appear, potentially allowing for earlier intervention 4, 8. However, markedly elevated levels (>25-30 ng/mL) are highly suggestive of metastatic cancer, particularly liver metastases 2, 4.