Carcinoembryonic Antigen (CEA) Unit Converter
Carcinoembryonic Antigen (CEA) Unit Converter
Convert CEA between ng/mL, µg/L and pmol/L against separate smoker and non-smoker reference limits, and see why CEA is a monitoring test rather than a screening one.
Carcinoembryonic Antigen (CEA) converter
Mass ⇄ molarCEA 2.1 ng/mL in an adult non-smoker
Formula and conversion factors
pmol/L = ng/mL × 5.5556
- ng/mL = µg/L
- identical concentrations, so no conversion is needed between them
- 5.55556
- derived from a molecular mass of 180,000 Da. CEA is heavily glycosylated, so treat the molar figure as nominal; no clinical threshold uses it
- smoking status
- the reference limit itself changes with smoking — commonly about 3 ng/mL in non-smokers and 5 ng/mL in smokers
- assay dependence
- CEA immunoassays are not harmonised; a change of platform can shift a serial trend, so follow a patient on one laboratory
Worked example
CEA 2.1 ng/mL in an adult non-smoker
2.1 ng/mL = 2.1 µg/L — the two units are identical
2.1 × 5.5556 = 11.7 pmol/L
Within the non-smoker reference interval of 0–3 ng/mL, and also below the 5 ng/mL smoker limit
Thresholds across the units
| ng/mL | pmol/L | |
|---|---|---|
| Adult non-smoker, upper reference limit | 3 | 16.7 |
| Adult smoker, upper reference limit | 5 | 27.8 |
| Rarely exceeded by benign disease | 10 | 55.6 |
| Often seen with metastatic disease | > 20 | > 111 |
Raised CEA without cancer
| Common benign causes | Typical effect |
|---|---|
| Cigarette smoking | Raises the baseline; the reason a separate smoker limit exists |
| Chronic obstructive pulmonary disease, chronic bronchitis | Modest persistent elevation |
| Cirrhosis, chronic hepatitis, biliary obstruction | Modest elevation, fluctuating with liver inflammation |
| Pancreatitis, peptic ulcer, diverticulitis | Transient elevation during the acute episode |
| Inflammatory bowel disease | Elevation tracking disease activity |
| Hypothyroidism, renal impairment | Reduced clearance or altered synthesis lifts the level |
Why the smoker's limit is a different number
CEA is reported in ng/mL and in the numerically identical µg/L, so there is nothing to calculate between those two. A pmol/L column uses a factor of 5.5556 from a molecular mass of 180,000 daltons, but CEA is heavily glycosylated and its true mass varies, so the molar figure should be read as nominal. No published threshold is expressed in molar units, and every decision made on CEA is made in ng/mL.
The reference limit is not a single number, because smoking raises CEA in people with no malignancy at all. Laboratories therefore quote separate limits: commonly about 3 ng/mL for non-smokers and about 5 ng/mL for smokers, though assay-specific figures such as 3.9 and 5.6 are also in use. Applying the non-smoker limit to a smoker converts an ordinary result into an abnormal one, and applying the smoker limit to a non-smoker does the reverse. The smoking history is part of the test.
CEA is a monitoring marker, not a screening one. Its established use is surveillance after curative resection of colorectal cancer, where a rising trend across serial samples can detect recurrence before it becomes clinically apparent, and assessment of response in metastatic disease. It is not recommended for detecting cancer in people without symptoms: around a third of colorectal cancers never raise it, poorly differentiated tumours in particular, so a normal CEA excludes nothing.
Two practical points follow. First, the trend matters more than the value, and the trend is only valid on one assay — CEA immunoassays are not harmonised, and a change of laboratory can produce an apparent rise or fall that reflects only the platform. Second, a modest elevation has a long list of benign explanations, from chronic obstructive pulmonary disease and cirrhosis to pancreatitis, inflammatory bowel disease and hypothyroidism, and benign disease rarely pushes CEA past about 10 ng/mL. A raised result is a prompt to see a clinician who can read it against the history, not a diagnosis.
Frequently asked questions
How do I convert CEA from ng/mL to pmol/L?
Multiply by 5.5556, derived from a molecular mass of 180,000 daltons. A CEA of 2.1 ng/mL is 11.7 pmol/L. Because CEA is heavily glycosylated the molar figure is nominal, and ng/mL — identical to µg/L — is the unit every threshold uses.
Why is the CEA limit higher for smokers?
Smoking raises CEA in people with no cancer, so laboratories publish separate upper limits: commonly around 3 ng/mL for non-smokers and 5 ng/mL for smokers. Reading a smoker’s result against the non-smoker limit makes an ordinary value look abnormal.
Can CEA be used to screen for bowel cancer?
No. It is not recommended for detecting cancer in people without symptoms. Around a third of colorectal cancers, particularly poorly differentiated ones, never raise CEA, and many benign conditions do. Its established role is surveillance after resection and monitoring metastatic disease.
What benign conditions raise CEA?
Smoking, chronic obstructive pulmonary disease, cirrhosis and chronic hepatitis, biliary obstruction, pancreatitis, peptic ulcer, diverticulitis, inflammatory bowel disease, hypothyroidism and renal impairment. Benign causes rarely take CEA beyond about 10 ng/mL.
Why does my CEA change when the laboratory changes?
CEA immunoassays are not harmonised between manufacturers, so the same sample can give different numbers on different platforms. Serial monitoring is only interpretable on one assay, and a change of laboratory can create an apparent trend that has nothing to do with the patient.
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References
- Locker GY, Hamilton S, Harris J, et al. ASCO 2006 update of recommendations for the use of tumor markers in gastrointestinal cancer. J Clin Oncol. 2006;24(33):5313–5327.
- Mayo Clinic Laboratories. Carcinoembryonic Antigen (CEA), Serum (test 8521): reference values ≤3.0 ng/mL in non-smokers; some smokers have values usually below 5.0 ng/mL.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.