What is a CEA (Carcinoembryonic Antigen) test?

What is a CEA Test?

The CEA (Carcinoembryonic Antigen) test is a blood test that measures levels of a glycoprotein tumor marker primarily used for monitoring treatment response and detecting recurrence in patients with known colorectal cancer, but it is not suitable for cancer screening or diagnosis due to its low sensitivity and specificity. 1, 2

Basic Characteristics of CEA

• CEA is a glycoprotein with a molecular weight of approximately 200,000, extracted from colonic cancer tissue, that can be detected and measured by radioimmunoassay 3
• Normal CEA levels are typically defined as less than 2.5-5 ng/mL, though the threshold varies between laboratories and countries 1, 3
• CEA is not cancer-specific and can be elevated in multiple malignant and benign conditions, which fundamentally limits its diagnostic utility 2, 3

Clinical Applications Where CEA Testing is Recommended

For Colorectal Cancer Patients

• Preoperative staging: CEA may be ordered before surgery if it would assist in staging and surgical planning, as elevated preoperative CEA (≥5 ng/mL) correlates with poorer prognosis 1
• Postoperative surveillance: CEA should be measured every 3 months for at least 3 years in patients with stage II or III colorectal cancer who are candidates for surgery or chemotherapy of metastatic disease 1
• Monitoring metastatic disease: CEA is the marker of choice for monitoring response to systemic therapy in metastatic colorectal cancer, measured at treatment initiation and every 1-3 months during active treatment 1, 2

For Other Cancers

• Breast cancer: CEA can be used for monitoring metastatic breast cancer during active therapy in conjunction with imaging, history, and physical examination, as levels are elevated in 50-60% of metastatic cases 4, 2
• Gallbladder cancer: CEA should be measured every 3-4 months during the first year post-surgery, every 6 months during the second year, and annually thereafter until 5 years, in combination with CA 19-9 and CA 125 5

Where CEA Testing is NOT Recommended

• CEA should never be used as a screening test for colorectal cancer because specificity is high but sensitivity is very low, particularly for early-stage disease 1, 2
• CEA should not be used for cancer diagnosis as only 50-60% of patients with metastatic colorectal cancer have elevated levels 2
• CEA elevation alone does not justify starting treatment for presumed metastatic disease without radiographic or pathologic confirmation 1, 4

Factors That Elevate CEA Without Cancer

Benign Medical Conditions

• Gastrointestinal diseases: Inflammatory bowel disease, gastritis, peptic ulcer disease, and pancreatitis can elevate CEA 4, 3
• Liver diseases: Cirrhosis, hepatitis, and benign biliary obstruction (especially with coexistent cholangitis or liver abscess) raise CEA levels 4, 3
• Pulmonary conditions: Chronic obstructive pulmonary disease and lung fibrosis are associated with elevated CEA 6
• Renal disease: Uremia can significantly increase CEA levels 6

Physiologic Factors

• Smoking history influences serum CEA levels and can cause elevations up to 10 ng/mL 3
• Aging is associated with increased CEA levels, with healthy individuals older than 65 years having higher median levels than younger adults 6

Critical Interpretation Pitfalls to Avoid

• Transient elevations during early chemotherapy: CEA may be spuriously elevated during the first 4-6 weeks of new therapy and should be interpreted with caution during this period 4, 2
• Progressive disease indication: Two CEA values above baseline are adequate to document progressive disease even without corroborating radiographs 1
• Post-surgical kinetics: Following complete tumor removal, CEA levels should fall to normal within 14 days in the majority of patients 7
• Confirmation requirement: An elevated CEA should be confirmed by retesting before proceeding with extensive workup for metastatic disease 4

When to Pursue Further Evaluation

• If CEA is elevated and confirmed on retesting, perform comprehensive imaging including CT scans of chest, abdomen, and pelvis to identify potential metastatic sites 4
• Focus on common metastatic sites for colorectal cancer including liver, lungs, and peritoneum 4
• Consider non-malignant causes before extensive oncologic workup, particularly in patients with known inflammatory, hepatic, or pulmonary conditions 4, 3