Cancer Antigen 15-3 (CA 15-3) Tumor Marker
This test measures the levels of a protein (CA 15-3) that may be produced by certain types of cancer, including breast cancer and other cancers of the female reproductive system. It helps doctors monitor treatment progress and check for recurrence.
["CA 15-3 helps track cancer progression and response to treatment by measuring a protein linked to certain cancers."]
Key facts at a glance
- LOINC
- 50776-4
- Short code
- CA153-CSF
- Synonyms
- Cancer Ag15-3 CSF-aCnc
- Category
- chemistry
- Sample
- csf
- Container
- Sterile CSF collection tube (polypropylene), tube 2 or 3 preferred for chemistry analysis
- Units
- N/A
- Ref low
- 15
- Ref high
- 3
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- female
- Age range
- 18–99 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86316
- SNOMED
- 115341000221101
- Specimen volume
- 1-2 mL of cerebrospinal fluid
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months
- Hemolysis max
- 200
- TAT
- 24–72 hours
- Order
- routine
What Is CA 15-3 Used For?
CA 15-3 is primarily used as a biomarker to assist in the diagnosis, monitoring, and follow-up of patients with breast cancer and other cancers that may produce this protein. It can also be used in screening and surveillance for patients at higher risk or who have had cancer treatment.
How Is the Test Performed?
A blood sample is drawn from a vein in your arm. The sample is then sent to a lab for analysis using an immunoassay method, which detects the presence of CA 15-3 protein in your blood.
What Does a High or Low Level Mean?
High levels of CA 15-3 may indicate the presence of cancer, especially in breast cancer or other cancers that produce this protein. However, it can also be elevated in other conditions like liver disease or pregnancy. Low levels do not necessarily mean cancer is absent, as levels can vary widely among individuals.
How Often Is This Test Done?
The frequency of CA 15-3 testing depends on your medical history, treatment plan, and doctor’s recommendations. It may be done regularly during cancer treatment to monitor response or after treatment to check for recurrence.
Reference range
Not established in cerebrospinal fluid; CA 15-3 is not normally present in CSF. Any detectable level should be interpreted in clinical context.N/A
No special patient preparation required. Lumbar puncture should be performed by qualified personnel following standard aseptic technique.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CA 15-3
Frequently asked questions
Why might my doctor order a CA 15-3 test?
Can CA 15-3 levels be affected by other conditions?
What should I expect during and after the blood draw?
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