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CA-125 (Serum) – Tumor Marker for Ovarian Cancer Screening

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

This blood test measures a protein (CA-125) that may be elevated in certain cancers, including ovarian cancer, and sometimes in other conditions affecting the ovaries, uterus, or peritoneum.

Quick summary

["CA-125 helps monitor cancer progression or response to treatment but is not a definitive diagnostic test alone."]

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

Key facts at a glance

LOINC
10334-1
Short code
CA125
Synonyms
Cancer Ag125 SerPl-aCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube; plasma may be collected in heparin or EDTA tubes
Units
N/A
Ref low
0
Ref high
35
Critical range
0.5 N/A – —
Fasting
false
Population
adult
Sex
female
Age range
≥ 18 years
Method
Immunoassay (chemiluminescent or electrochemiluminescent)
CPT
86304
SNOMED
1152695009
Specimen volume
1 mL serum or plasma
Stability
Stable for 24 hours at room temperature (15-25°C), 7 days refrigerated (2-8°C), and 3 months frozen at -20°C or colder. Avoid repeated freeze-thaw cycles.
Hemolysis max
500
Lipemia max
1000
Icterus max
25
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 in other gynecologic cancers. It may also help track how a cancer is responding to treatment or detect recurrence. However, it is not a standalone test for diagnosing ovarian cancer, as other conditions can also raise its levels.

How Is the Test Performed?

A small blood sample is drawn from a vein, usually in your arm. The blood is sent to a lab where it is tested for the CA-125 protein using an immunoassay method. Results are reported in units per liter (U/L).

When Might You Need This Test?

Your healthcare provider may order a CA-125 test if you have symptoms like abdominal pain, bloating, or changes in bowel habits. It may also be used in screening high-risk individuals (e.g., those with a family history of ovarian cancer) or as part of follow-up for ovarian cancer patients.

What Do Results Mean?

Elevated CA-125 levels may indicate ovarian cancer or other conditions like endometriosis, pelvic inflammatory disease, or liver disease. However, a normal result does not rule out ovarian cancer. Interpretation depends on clinical context, including symptoms, medical history, and imaging results.

Reference range

Normal: <35 U/mL. Values may vary by laboratory methodology and reference population.N/A

Specimen: serum

No special preparation required. Specimen collection is not affected by recent food intake or fasting status.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: CA-125 plays a key role in ovarian cancer surveillance but lacks specificity. It is often used alongside other tests (e.g., ultrasound, CA-125 screening algorithms) for better accuracy. False positives and negatives can occur, so results should be reviewed by a healthcare provider.

Short name

CA-125

Frequently asked questions

Why might my CA-125 test be ordered if I don’t have symptoms?
Your doctor may recommend it as part of routine screening for ovarian cancer, especially if you have a higher risk due to family history, genetic mutations (e.g., BRCA), or other factors. It can also be used to monitor existing cancer or related conditions.
Can CA-125 levels change over time, and what does that mean?
Yes, CA-125 levels can fluctuate due to cancer progression, treatment effects, or other health changes. A rising level may suggest cancer growth or recurrence, while a falling level could indicate treatment success. Always discuss changes with your provider.
Are there any side effects or risks from this blood test?
The blood draw is generally safe but may cause mild discomfort or bruising at the site. Rarely, there could be infection or excessive bleeding. No other side effects are typically associated with the CA-125 test itself.
  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