What is this test?
CA 15-3 is a protein marker that can be elevated in some people with breast cancer and in several other conditions. It is used mainly for monitoring.
Why might it be ordered?
- To monitor the effect of treatment in certain cases of established breast cancer.
- For follow-up over time along with examination and imaging studies.
What sample is needed?
A healthcare professional collects a venous blood sample. Depending on the method, the laboratory uses serum or plasma.
How should you prepare?
Tell the laboratory about all medicines, hormone treatments, vitamins and supplements you take. Do not stop or change treatment unless your clinician tells you to. Follow any instructions about fasting and the time of collection.
How should you understand the result?
There may also be an increase in benign diseases of the breast, liver, pregnancy and other conditions. A trend across consecutive measurements made with a comparable method is often more informative than a single value.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.