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Ovarian Cancer Antigen 125 (CA 125), Serum/Plasma

Published: August 9, 2026Updated: August 16, 2026

A blood test that measures CA-125, a protein that may be elevated in ovarian cancer and several noncancerous conditions. It is mainly used to monitor people with known ovarian cancer.

Quick summary

["CA-125 can help track ovarian cancer, but an elevated result does not by itself diagnose cancer."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
11659-0
Short code
Ovarian a-R Vmin dias DOP
Synonyms
Ovarian a-R Vmin dias DOP
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-doppler
CPT
86038
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

The CA-125 test measures a protein called cancer antigen 125 in blood. This protein is produced by some normal tissues as well as by certain cancers, including ovarian cancer.

Why might I need this test?

CA-125 is most often used to check whether treatment for known ovarian cancer is working and whether the cancer may be progressing. A clinician may also order it when evaluating an ovarian mass or symptoms that could be related to ovarian cancer.

How is the test performed?

A blood sample is collected, and the laboratory measures the amount of CA-125 in the serum or plasma. Results are interpreted along with your symptoms, examination findings, imaging, and other laboratory tests.

How do I prepare for the test?

Fasting is usually not required for a CA-125 blood test. Tell your healthcare professional if you are menstruating, pregnant, or recently had pelvic surgery, because these circumstances can affect the result.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

An elevated CA-125 level may occur with ovarian cancer, but it can also result from endometriosis, pelvic inflammatory disease, menstruation, pregnancy, and other benign or malignant conditions. A high result does not establish a cancer diagnosis and should be interpreted with other clinical information. A result within the laboratory's reference range does not completely rule out ovarian cancer.

Short name

CA 125

Frequently asked questions

Does an elevated CA-125 level mean I have ovarian cancer?
No. Many noncancerous conditions can raise CA-125, so an elevated result usually requires further evaluation rather than establishing a diagnosis by itself.
Is CA-125 recommended for routine ovarian cancer screening?
It is generally not used alone to screen people who do not have symptoms or a known ovarian cancer. CA-125 is most useful for evaluating specific concerns and monitoring known disease.
Do I need to fast before the test?
Fasting is usually unnecessary. Follow any instructions provided by your healthcare professional or laboratory.
  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 16, 2026. · Read our editorial policy