Carcinoembryonic Antigen (CEA)
The CEA test measures serum carcinoembryonic antigen, a glycoprotein tumour marker elevated in colorectal, gastric, pancreatic, lung, and breast cancers. It is used to monitor treatment response and detect recurrence in known malignancy, not as a screening tool, since benign inflammatory disease and smoking also raise CEA and many early cancers produce normal levels.
1
Biomarkers
Blood (serum)
Sample
1–2 business days
Turnaround
No
Fasting
What is the CEA test?
The Carcinoembryonic Antigen (CEA) test quantifies a glycoprotein tumour marker that, while present at low levels in healthy adults, is elevated in a subset of malignancies — most notably colorectal, gastric, pancreatic, lung, and breast cancers. Because CEA can be raised by benign inflammatory and smoking-related conditions and because many early cancers do not produce it, the test is not recommended for screening; instead, it is ordered to monitor known malignancy and to detect recurrence after curative-intent therapy. In the surveillance paradigm a baseline CEA is measured before treatment, and serial post-treatment measurements track the tumour burden over time. A rising CEA after resection or systemic therapy is an early signal of recurrence, prompting imaging and intervention before clinical symptoms appear. Practitioners rely on kinetics — the doubling time and persistence of elevation — rather than a single value, since absolute thresholds cannot distinguish residual disease from benign fluctuation without context.
What does the CEA test measure?
Carcinoembryonic antigen is a glycoprotein involved in cell adhesion, expressed during foetal development and normally repressed after birth. It is produced by gastrointestinal epithelium and to a lesser extent by bronchial, breast, and pancreatic tissues. In adults low concentrations circulate in healthy individuals, particularly smokers, while malignant transformation and certain benign inflammatory states can de-repress CEA synthesis and shed large amounts into the bloodstream. Its plasma half-life is approximately one week, so changes in tumour burden are reflected slowly in serial measurements.
CEA is a tumour-associated antigen used primarily to monitor treatment response and detect recurrence in colorectal and other gastrointestinal malignancies. It lacks the sensitivity and specificity to serve as a screening test in asymptomatic populations, since benign gastrointestinal, hepatobiliary, and pulmonary diseases, as well as smoking, can elevate it and many early-stage cancers produce normal levels. When a colorectal cancer is known to secrete CEA, serial measurements are the standard of care for post-resection surveillance, where a rising trend prompts imaging to investigate recurrence.
Why is the CEA test ordered?
- Post-surgical monitoring of patients with resected colorectal cancer who had elevated preoperative CEA, measured every three to six months for surveillance
- Assessment of treatment response in metastatic colorectal, gastric, or pancreatic adenocarcinoma, interpreted alongside imaging
- Investigation of suspected recurrence when a previously normalised CEA begins to rise or when imaging findings are equivocal
- Baseline measurement before starting therapy for gastrointestinal malignancy, to establish whether CEA is a useful marker for that individual
- Monitoring of non-small-cell lung cancer or breast cancer when the tumour is known to secrete CEA and other markers are not available or informative
- Evaluation of a patient with metastatic adenocarcinoma of unknown primary, where CEA may support a gastrointestinal or pulmonary source in conjunction with imaging and histology
- Investigation of unexplained persistent elevation in a patient with risk factors or symptoms, though always interpreted with imaging and colonoscopy rather than as a standalone diagnostic
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
1–2 business days
Collection notes
Phlebotomy via LabCorp draw site; no special preparation required. Serial measurements for surveillance should be performed at the same laboratory using the same assay platform to ensure comparability.
Specimen requirements
Minimum 0.5 mL serum (gel separator acceptable). Separate from cells promptly; CEA is stable refrigerated for several days and can be frozen for longer-term storage if needed.
What can affect CEA results?
Smokers have higher baseline CEA due to bronchial epithelial production; the reference limit for smokers is typically raised to around 5 ng/mL to account for this physiological elevation.
Inflammatory bowel disease, pancreatitis, cirrhosis, and biliary obstruction can all raise CEA modestly, so the test must be interpreted with clinical context and imaging.
Chronic obstructive pulmonary disease, pneumonia, and pulmonary fibrosis can elevate CEA, overlapping with lung malignancy and requiring imaging correlation.
Reduced clearance in hypothyroid states can modestly raise CEA; thyroid function should be assessed if elevation is unexplained.
CEA may transiently rise in the immediate post-operative period due to tumour manipulation or cell death; a nadir is usually reached four to six weeks after surgery, so serial measurement starts thereafter.
CEA assays are not fully standardised, so results are not interchangeable across laboratories; serial monitoring should use the same platform and reference the same performing lab.
What do CEA results mean?
Elevated
Malignancy: colorectal, gastric, pancreatic, lung (adenocarcinoma), breast, ovarian, and medullary thyroid cancers. Metastatic disease elevates CEA more reliably than localised disease. Benign causes: inflammatory bowel disease, pancreatitis, cirrhosis, biliary obstruction, chronic obstructive pulmonary disease, and smoking. Magnitude and trend matter — a persistently rising CEA after treatment is more concerning than a static modest elevation.
Normal
A normal CEA does not exclude malignancy — many early-stage and some advanced cancers do not secrete CEA. It is most useful in patients with a known elevated preoperative level, where serial normal results provide reassurance of disease control.
Reduced
Falling CEA after surgery or systemic therapy indicates response and reduced tumour burden. The goal post-resection is normalisation to below the reference limit; the nadir level then becomes the individual's baseline for surveillance.
Note: CEA is a monitoring tool, not a diagnostic test. Interpret serially rather than as a single snapshot, always in conjunction with imaging and clinical assessment. Assay platforms differ, so compare results within the same laboratory. Smoking status must be considered when applying reference limits.
Frequently asked questions
CEA is used primarily to monitor colorectal cancer and is also elevated in gastric, pancreatic, lung (adenocarcinoma), breast, ovarian, and medullary thyroid cancers. It is most useful when the tumour is known to secrete CEA at diagnosis.
How to access the CEA test
The CEA reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- National Comprehensive Cancer Network. NCCN clinical practice guidelines in oncology: colon cancer. (2025)
- Locker GY, et al. ASCO guideline on the use of tumour markers in gastrointestinal cancers. J Clin Oncol. (2006)
- Duffy MJ, et al. Tumour markers in colorectal cancer, gastric cancer, and gastrointestinal stromal cancers: European Group on Tumour Markers (EGTM) guideline update. Int J Cancer. (2020)
- Sturgeon CM, et al. National Academy of Clinical Biochemistry laboratory medicine practice guidelines for use of tumour markers in testicular, prostate, colorectal, breast, and ovarian cancers. Clin Chem. (2008)
- Nicholson BD, et al. Blood CEA levels for detecting recurrent colorectal cancer. Cochrane Database Syst Rev. (2015)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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