Cancer Antigen 15-3 (CA 15-3) Tumor Marker
This blood test measures levels of a protein (CA 15-3) that may be produced by certain types of cancer, including breast cancer and some others.
["CA 15-3 helps monitor cancer progression or treatment response in some patients."]
Key facts at a glance
- LOINC
- 50778-0
- Short code
- CA15-3 PER
- Synonyms
- Cancer Ag15-3 Prt-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Sterile, leak-proof container without anticoagulants (e.g., red-top vacutainer or sterile urine container); chemistry/sterile tube preferred
- Units
- N/A
- Ref low
- 15
- Ref high
- 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
- 104642001
- Specimen volume
- 5-10 mL of peritoneal fluid
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months (avoid repeated freeze-thaw cycles)
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 24–72 hours
- Order
- routine
What Is CA 15-3 Used For?
CA 15-3 is often used as a biomarker to track the activity of certain cancers, particularly in patients who have already been diagnosed. It may also be used in follow-up care to check for signs of recurrence after treatment. However, it is not a standalone test for diagnosing cancer and should be interpreted alongside other clinical findings and tests.
How Is the Test Performed?
A blood sample is taken from a vein in your arm. The blood is sent to a lab where it is analyzed for CA 15-3 levels using an immunoassay method. This test does not require fasting.
What Might Affect Test Results?
Several factors could influence CA 15-3 levels, including certain medications, liver disease, obesity, and hormonal changes. If you are pregnant or have known health conditions, let your healthcare provider know before the test.
What Do Results Mean?
Higher than usual levels of CA 15-3 may suggest the presence of cancer, but they can also be elevated in other conditions. Your doctor will consider your medical history, symptoms, and other test results to interpret the results accurately.
Reference range
CA 15-3 is not typically measured in peritoneal fluid as a standard reference range exists; peritoneal fluid CA 15-3 levels are generally interpreted in conjunction with serum levels and clinical context. Elevated levels may suggest peritoneal involvement by malignancy.N/A
No special patient preparation required. Peritoneal fluid is typically collected via paracentesis performed by a qualified healthcare provider.
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 change over time?
Is there anything I should do before the test?
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