CA 125 Tumor Marker (Serum) – Fluid
This test measures the CA 125 protein, which is often elevated in certain cancers, including ovarian cancer, but can also appear in other conditions.
["CA 125 helps doctors monitor cancer progression or response to treatment."]
Key facts at a glance
- LOINC
- 11210-2
- Short code
- CA125
- Synonyms
- Cancer Ag125 Fld-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top serum tube or SST (serum separator tube)
- Units
- N/A
- Ref low
- 0
- Ref high
- 35
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- female
- Age range
- 18–65 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86304
- SNOMED
- 104686001
- Specimen volume
- 1-2 mL serum
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is CA 125 Used For?
CA 125 is primarily used as a screening or monitoring tool for ovarian cancer and sometimes for other gynecologic cancers. It may also help track how well treatment is working or detect recurrence. However, it is not a definitive diagnostic test on its own and is often used alongside other tests and imaging.
How Is the Test Performed?
A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab for analysis. The test looks for the CA 125 protein in your serum (the liquid part of blood after clotting).
What Might Affect Results?
Several factors can influence CA 125 levels, including certain medical conditions (like endometriosis, pelvic inflammatory disease, or benign ovarian cysts), pregnancy, and some medications. Always inform your healthcare provider about any conditions or treatments you’re receiving.
When Might You Need This Test?
You may need a CA 125 test if you have symptoms of ovarian cancer (such as bloating, pelvic pain, or unexplained weight loss), if you’re at higher risk due to family history, or as part of routine monitoring for cancer treatment.
Reference range
Reference values vary by specimen type and laboratory. Generally <35 U/mL in serum is considered normal for healthy adults. Body fluid values should be interpreted in clinical context with paired serum measurements.N/A
No special preparation required. Specimen should be collected prior to initiation of chemotherapy or radiotherapy when possible for baseline assessment.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CA 125
Frequently asked questions
Why might my CA 125 test result be higher than expected?
Can CA 125 levels go back to normal after treatment?
Is CA 125 a reliable test for diagnosing ovarian cancer?
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