Serum/plasma mass concentration of cancer antigen 15.3 (CA 15.3)
This test measures the amount of a specific protein, called cancer antigen 15.3, in your blood. It may help detect or monitor certain types of cancer, such as breast cancer.
["CA 15.3 can sometimes rise in people with breast cancer or other cancers, but it’s not always a definitive sign of cancer alone."]
Key facts at a glance
- LOINC
- 6875-9
- Short code
- CA15-3
- Synonyms
- Cancer Ag15-3 SerPl-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube
- Units
- N/A
- Ref low
- 0
- Ref high
- 30
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86300
- SNOMED
- 115341004
- Specimen volume
- 1 mL serum
- Stability
- Stable for 7 days at 2-8°C; 3 months at -20°C; avoid repeated freeze-thaw cycles
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 4–24 hours
- Order
- routine
What Is CA 15.3 Used For?
CA 15.3 is often used as a **tumor marker**—a substance produced by some cancer cells. While it can help track cancer progression or response to treatment in some patients, it’s not a standalone test for diagnosis. Doctors may use it alongside other tests, like imaging or biopsies, to assess cancer spread or recurrence.
How Is the Test Performed?
A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab to measure the protein levels. Results are reported in units of mass concentration (often in kilograms per liter or micrograms per milliliter, though exact units may vary).
Why Might Your Doctor Order This Test?
Your doctor may order CA 15.3 testing if you have a history of breast cancer, are being monitored for recurrence, or have symptoms that could suggest cancer, such as unexplained weight loss, pain, or changes in breast tissue. It can also be used during treatment to check how well your body is responding.
What Does a High or Low Level Mean?
Elevated levels of CA 15.3 may indicate cancer, but they can also be raised in other conditions, like pregnancy, liver disease, or certain infections. Low levels don’t always mean cancer is gone, as some people with cancer have normal levels. Results should always be interpreted by a healthcare provider in the context of your overall health.
Reference range
< 30 U/mL (commonly used clinical cutoff; method-dependent)N/A
No special patient preparation required. Fasting is not required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: Limitations and Considerations
Short name
CA 15.3
Frequently asked questions
How often will I need this test?
Can diet or medications affect this test?
Is this test always accurate?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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