Unit Converter
Carcinoembryonic antigen (CEA)
(Oncofetal Glycoprotein – Tumor Marker for Colorectal & GI Cancers)
Synonyms
- CEA
- Carcinoembryonic antigen
- CEACAM-5
- GI tumor marker
- Oncofetal antigen
Units of Measurement
- µg/L
- ng/L
- ng/dL
- ng/100 mL
- ng%
- ng/mL
1 ng/mL = 1 µg/L
ng/dL = ng/100 mL = ng%
Description
CEA is a large cell-surface glycoprotein involved in cell adhesion.
It is normally produced during fetal development, but low levels persist in healthy adults.
CEA is most useful as a tumor marker for:
- Colorectal cancer (primary use)
- Gastrointestinal cancers
- Monitoring recurrence after surgery
- Evaluating treatment response
It is not a screening test due to low sensitivity.
Physiological Source
Produced by epithelial cells of:
- Colon
- Stomach
- Pancreas
- Lung
- Breast
CEA increases significantly in malignancy due to increased gene expression and tumor shedding.
Clinical Significance
Elevated CEA
1. Colorectal Cancer (Most Important Use)
CEA is used for:
- Baseline tumor marker at diagnosis
- Monitoring treatment response
- Detecting recurrence after resection
- Surveillance for metastasis (especially liver/lung)
CEA elevation correlates with tumor burden.
2. Gastrointestinal Cancers
Elevated in:
- Gastric cancer
- Pancreatic cancer
- Esophageal cancer
- Cholangiocarcinoma
3. Lung Cancer
Particularly adenocarcinoma.
4. Breast, Thyroid, Cervical Cancers
Occasional increases.
5. Benign Diseases (usually mild elevation, <10 ng/mL)
- Smoking
- Cirrhosis
- IBD (Crohn, UC)
- Pancreatitis
- COPD
- Hypothyroidism
Low CEA
Normal; does not rule out cancer.
Early-stage tumors may not elevate CEA.
Reference Intervals
(Tietz 8E + NCCN + ASCO + Mayo + ARUP)
Non-smokers
- < 3 ng/mL (≈ <3 µg/L)
Smokers
- < 5 ng/mL (≈ <5 µg/L)
Interpretation
- 3–10 ng/mL → borderline; consider benign conditions or smoking
- >10 ng/mL → suspicious for malignancy
- >20 ng/mL → likely metastatic disease
- >100 ng/mL → strongly suggests advanced cancer (often liver metastasis)
Postoperative
- Successful resection → CEA should normalize within 4–6 weeks
- Rising trend → recurrence
Unit Meanings
| Unit | Meaning |
| µg/L | microgram per liter |
| ng/L | nanogram per liter |
| ng/mL | nanogram per milliliter |
| ng/dL | nanogram per deciliter |
| ng/100 mL | same as ng/dL |
| ng% | same as ng/dL |
Diagnostic Uses
1. Monitoring Colorectal Cancer
Most important use:
- CEA decreases with effective therapy
- CEA doubling → recurrence
- Used in NCCN surveillance schedules
2. Post-Surgical Surveillance
Every 3–6 months for 3–5 years.
3. Evaluating Treatment Response
- Chemotherapy
- Radiation
- Targeted therapy
4. Metastatic Disease Assessment
Rising CEA often precedes radiologic detection.
5. Adjunct Marker
Used with:
- CA 19-9 (pancreas)
- CA 72-4 (gastric)
- AFP (liver)
Not diagnostic alone.
Analytical Notes
- Immunoassay-based
- Hemolysis minimal effect
- Avoid interpretation in heavy smokers (higher baseline)
- CEA should be interpreted with imaging and clinical context
- Tumor marker assays vary between labs; use same assay for serial tests
Clinical Pearls
- CEA is best for monitoring, not diagnosis.
- Smoking increases CEA by ~20–30%.
- CEA >20 ng/mL strongly suggests metastatic GI cancer.
- Normal CEA does NOT exclude colorectal cancer.
- Postoperative rising CEA is one of the earliest markers of recurrence.
Interesting Fact
CEA was discovered in 1965 as one of the first “tumor antigens,” helping launch the modern field of tumor markers and immunoassays.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Tumor Markers.
- NCCN Colorectal Cancer Surveillance Guidelines.
- ASCO Tumor Marker Recommendations.
- IFCC - Tumor Marker Harmonization.
- Mayo Clinic Laboratories - CEA.
- ARUP Consult - CEA Testing.
- MedlinePlus / NIH - CEA Overview.