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Cancer Antigen 15-3 (CA 15-3) Tumor Marker

Published: August 9, 2026Updated: August 17, 2026

This blood test measures a protein produced by some cancer cells, often linked to breast cancer but also found in other conditions.

Quick summary

["CA 15-3 helps track cancer progression or response to treatment in certain cancers."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
29153-4
Short code
CA153BF
Synonyms
Cancer Ag15-3 Fld-aCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red top tube
Units
N/A
Ref low
0
Ref high
31.3
Critical range
0.5 N/A – —
Fasting
false
Population
adult
Sex
female
Age range
≥ 18 years
Method
Immunoassay (Chemiluminescent or Electrochemiluminescent)
CPT
86300
SNOMED
11526-1
Specimen volume
1 mL serum (minimum 0.5 mL)
Stability
Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 3 months
Hemolysis max
100
Lipemia max
200
Icterus max
50
TAT
4–24 hours
Order
routine

What Is CA 15-3 Used For?

CA 15-3 is primarily used as a biomarker to monitor breast cancer recurrence or progression, especially in patients who have undergone treatment. It may also be checked in other cancers, such as ovarian or pancreatic, though its role varies by diagnosis. Levels can sometimes rise with other conditions like benign breast disease or liver disease, so results are interpreted alongside clinical findings and other tests.

How Is CA 15-3 Tested?

The test involves drawing blood from a vein in your arm. The blood is sent to a lab, where it is analyzed using an immunoassay method to detect the CA 15-3 protein. Results are reported as a numerical value, though reference ranges can vary by lab and may not apply to everyone.

Why Might Your Doctor Order This Test?

Your doctor may order a CA 15-3 test if you have a history of breast cancer, are undergoing treatment, or have symptoms that could suggest cancer recurrence. It may also be used as part of routine monitoring in certain cancer surveillance programs or when evaluating symptoms like breast pain, weight loss, or fatigue.

What Do CA 15-3 Results Mean?

Higher-than-normal levels of CA 15-3 may indicate cancer activity, but they can also be elevated in other health conditions. A single test result alone is not diagnostic—your doctor will consider your overall health, medical history, and other test results to interpret the meaning.

Reference range

< 31.3 U/mL (healthy individuals); values may vary by laboratory and analytical methodN/A

Specimen: serum

No special preparation required. CA 15-3 levels are not significantly affected by recent meals.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: CA 15-3 plays a key role in tracking breast cancer progression or response to therapy, particularly in patients with metastatic disease. While it is not a definitive test for cancer detection, rising levels over time may signal recurrence. False elevations can occur in non-cancerous conditions, so results must be evaluated carefully in context.

Short name

CA 15-3

Frequently asked questions

Can CA 15-3 levels change with diet or lifestyle?
No, CA 15-3 levels are not directly influenced by diet or lifestyle factors like exercise or weight. However, certain medications (e.g., steroids) or health conditions (e.g., liver disease) may affect test results, so inform your doctor about all medications and conditions before testing.
What if my CA 15-3 level is high?
A high CA 15-3 level may raise concerns about cancer recurrence, but it does not confirm a diagnosis. Your doctor will review your medical history, symptoms, and other tests to determine the next steps, which may include additional imaging, further blood tests, or a biopsy.
How often should I get a CA 15-3 test?
The frequency depends on your medical history and treatment plan. If you have a history of breast cancer, your doctor may recommend monitoring every few months or as needed. Always follow your healthcare provider’s guidance for test timing.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy