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CA 125 Tumor Marker (Serum)

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of CA 125, a protein often produced by certain types of ovarian cancer and sometimes by other cancers or conditions affecting the female reproductive system.

Quick summary

["CA 125 helps monitor cancer progression or treatment response in some cases."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
2006-5
Short code
CA125
Synonyms
Cancer Ag125 SerPl Ql
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube; plasma acceptable in lithium heparin or EDTA tube
Units
N/A
Ref low
0
Ref high
35
Critical range
0.5 N/A – —
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Immunoassay (Chemiluminescent or Electrochemiluminescent)
CPT
86304
SNOMED
104935009
Specimen volume
1 mL serum or plasma (minimum 0.5 mL)
Stability
Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
1000
Icterus max
40
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, though it is not a definitive diagnostic test on its own. It may also be checked in patients with symptoms suggestive of ovarian or other gynecologic cancers, or in those undergoing treatment for these conditions. Levels can sometimes rise with other conditions, such as endometriosis or benign ovarian cysts, so results should be interpreted by your healthcare provider in the context of your overall health and medical history.

How Is the Test Collected?

A blood sample is drawn from a vein, usually in your arm, by a healthcare professional. You may feel a small pinch when the needle is inserted, but the procedure is quick and typically not painful afterward.

When Might You Need This Test?

Your doctor may recommend a CA 125 test if you have symptoms like persistent abdominal pain, bloating, or unexplained weight loss. It may also be part of routine monitoring for ovarian cancer patients or those with a family history of the disease. Always discuss test results with your healthcare provider to understand their relevance to your situation.

What Are Common Results?

Results are reported in international units per milliliter (IU/mL). Higher than normal levels may indicate ovarian cancer or other conditions, but they can also be elevated in non-cancerous situations. Your doctor will review your results with you and may recommend additional testing if needed.

Reference range

Normal: < 35 U/mL. Values above 35 U/mL may indicate malignancy or other conditions; clinical correlation required.N/A

Specimen: serum

No fasting required. Specimen collection may be performed at any time of day. Inform clinician of any recent pelvic examination, menstruation, or pregnancy as these may affect results.

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 be ordered if I don’t have symptoms of cancer?
Your doctor may order this test for routine monitoring if you have a history of ovarian cancer, are at high risk due to family history, or are undergoing treatment for other gynecologic conditions. It can also be part of follow-up care for conditions like endometriosis or pelvic inflammatory disease.
Can CA 125 levels be affected by other medications or health conditions?
Yes, certain medications (like birth control pills or hormonal therapies) and conditions (such as endometriosis, fibroids, or liver disease) may influence CA 125 levels. Always inform your healthcare provider about all medications and health conditions before testing.
Is a CA 125 test always accurate, even if it’s positive?
No, CA 125 is not a definitive diagnostic test for cancer. False positives can occur, and some cancers (like lung or breast cancer) rarely produce high levels of CA 125. Your doctor will use test results alongside other diagnostic tools, like imaging or biopsies, to make an accurate assessment.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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