CA 15-3
CA 15-3 is a protein produced by breast cells. This test measures CA 15-3 levels in the blood and is primarily used to monitor treatment response in patients with advanced breast cancer.
Category: Tumor Markers
Also known as: ca 15-3, ca15-3, ca 15 3, cancer antigen 15-3
Reference range: 0–30 U/mL (Source: ABIM)
Standard unit: U/mL
High values may indicate
High CA 15-3 levels may indicate breast cancer (especially metastatic), ovarian cancer, lung cancer, or non-cancerous conditions such as liver disease, lupus, or benign breast disease.
Low values may indicate
Low CA 15-3 levels are normal and may indicate a good response to breast cancer treatment in patients being monitored.
Frequently asked questions
- What is a normal CA 15-3 level?
- A typical reference range for CA 15-3 is 0–30 U/mL (source: ABIM). Reference ranges vary by laboratory, age, and sex, so always compare against the range on your own lab report.
- What units is CA 15-3 measured in?
- CA 15-3 is most commonly reported in U/mL. Labs in different countries may use other units — you can convert between them with BloodId's blood test unit converter.
- Where do CA 15-3 reference ranges come from?
- BloodId uses ABIM standard reference ranges and educational information from MedlinePlus (see our methodology). Reference ranges still vary by lab, age, and sex, so always compare against your own report.
- Can I track CA 15-3 over time?
- Yes. Upload results from any lab and BloodId charts your CA 15-3 over time against its reference range, so you can see whether the trend is rising, falling, or stable.