Cancer Antigen 125 (Mucin 16) - Serum/Plasma
This test measures a protein produced by some cancer cells and certain healthy tissues, often used to monitor ovarian, endometrial, or other gynecologic cancers.
["CA 125 helps track cancer progression and response to treatment."]
Key facts at a glance
- LOINC
- 50782-2
- Short code
- CA27-29 CSF
- Synonyms
- Cancer Ag27-29 CSF-aCnc
- Category
- chemistry
- Sample
- csf
- Container
- Sterile CSF collection tube (polypropylene, screw-cap)
- Units
- N/A
- Ref low
- 0
- Ref high
- 38.6
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–99 years
- Method
- Immunoassay (Chemiluminescent or Radioimmunoassay)
- CPT
- 86316
- SNOMED
- 39470006
- Specimen volume
- 1-2 mL
- Stability
- Room temperature: 2 hours; Refrigerated (2-8°C): 24 hours; Frozen (-20°C or below): 1 month
- Hemolysis max
- 200
- TAT
- 24–72 hours
- Order
- routine
What Is CA 125 Used For?
CA 125 is primarily used in the monitoring of ovarian cancer and other gynecologic cancers, such as endometrial cancer. It may also be checked after treatment to see if cancer has returned. However, CA 125 can also be elevated in other conditions, like benign cysts or fibroids, so it’s not definitive on its own.
When Might You Need This Test?
Your doctor may order a CA 125 test if you have symptoms like abdominal pain, bloating, or irregular bleeding, especially if you have a history of ovarian or endometrial cancer. It’s also used as part of follow-up testing after cancer treatment.
What to Expect During the Test
A blood sample is taken from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The blood is then sent to a lab for analysis.
Possible Results and Next Steps
Results are not always clear-cut. High levels may suggest cancer or other conditions, while low levels may mean cancer is under control. Your doctor will discuss the results in the context of your medical history and other tests.
Reference range
Not normally detectable in cerebrospinal fluid; results should be interpreted in conjunction with clinical findings, imaging, and cytology.N/A
No special preparation required. Inform physician of any medications or recent procedures.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CA 125
Frequently asked questions
Why is CA 125 important in cancer care?
How does CA 125 compare to other cancer tests?
Can CA 125 levels change over time?
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.
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Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy