Cancer antigen 125 (CA 125) screening test
This test measures the levels of a protein called cancer antigen 125 in your blood. It may be used as part of monitoring for certain cancers or to check for early signs of recurrence.
["CA 125 helps track ovarian, peritoneal, or other gynecologic cancers, but it’s not a definitive test for cancer diagnosis alone."]
Key facts at a glance
- LOINC
- 68925-7
- Short code
- CA724-CSF
- Synonyms
- Cancer Ag72-4 CSF-aCnc
- Category
- chemistry
- Sample
- csf
- Container
- Sterile CSF collection tube (polypropylene)
- Units
- N/A
- Ref low
- 0
- Ref high
- 6
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Electrochemiluminescence Immunoassay (ECLIA)
- CPT
- 86316
- SNOMED
- 115341000
- Specimen volume
- 1.0-2.0 mL of cerebrospinal fluid
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 6 months
- Hemolysis max
- 200
- TAT
- 24–72 hours
- Order
- routine
What Is CA 125 Used For?
CA 125 is primarily used in the context of ovarian cancer screening and surveillance. It may also be checked in patients with known gynecologic cancers to monitor for recurrence or spread. Some doctors use it as part of a broader evaluation for other conditions, such as endometriosis or peritoneal mesothelioma, though these uses are less common.
How Is the Test Performed?
A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab for analysis. CA 125 levels are measured using an immunoassay method, which detects the protein in your blood.
What to Expect Before the Test
There are no special preparations needed for this test. You can eat, drink, or take medications as usual. If you’re on blood thinners, let your healthcare provider know before the test.
Potential Side Effects
Most people experience only minor discomfort from the needle stick, which may include slight bruising or swelling at the injection site. Rarely, some people may feel lightheaded or dizzy.
Reference range
Not established for cerebrospinal fluid; serum reference: <6.0 U/mL. CSF values are typically lower than serum and clinical interpretation requires correlation with imaging and cytology.N/A
No special patient preparation required. Fasting is not necessary.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
CA 125 is a marker often elevated in ovarian cancer and other gynecologic cancers. While it can signal potential cancer activity, it is not specific to cancer alone. High levels may also be found in conditions like endometriosis, pelvic inflammatory disease, or other benign conditions. Doctors use CA 125 alongside other tests, imaging, and clinical findings to make a diagnosis or assess treatment progress. It is most useful in monitoring known cancer cases for recurrence or progression.
Short name
CA 125 Screening
Frequently asked questions
Why might my doctor order a CA 125 test?
What do CA 125 levels mean?
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.
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