What does it measure?
CA 125 is a protein-related marker that can enter the blood from several tissues. It is often used to monitor treatment in someone with a known ovarian cancer or to add context when a clinician is evaluating a specific ovarian finding.
Before the test
- Sample
- A blood sample from a vein.
- Context
- Mention menstruation, pregnancy, symptoms, and any previous ovarian treatment.
What can the result mean?
A high result can occur with ovarian cancer, but also with endometriosis, menstruation, pregnancy, and other noncancerous conditions. A low result does not rule out ovarian cancer. It is not suitable as a stand-alone cancer diagnosis or routine screening test for average-risk people without symptoms. [1]
When is it useful, and how is it read?
Separate monitoring a known ovarian cancer from evaluating symptoms or an ovarian mass. Menopausal status, pregnancy, cycle timing, examination, and imaging determine how much the result adds; routine testing in average-risk people without symptoms is a different situation. [1]
What can affect it?
Menopausal status, cycle timing, symptoms, imaging, and treatment history change the interpretation. Trends in a known condition can be more useful than a single reading. Methods can vary across laboratories. [1]
Myth: «A normal CA 125 rules out ovarian cancer»
Some ovarian cancers do not raise CA 125, while several noncancerous conditions can raise it. The result cannot replace assessment of persistent symptoms or an ovarian finding on imaging. [1]
Questions you might have
Can menstruation or endometriosis raise CA 125?
Yes. Several noncancerous conditions can raise it, so a high result is not a diagnosis of ovarian cancer. [1]
Can I use it as a routine cancer check without symptoms?
It is not an effective stand-alone screening test for people at average risk. Symptoms or inherited risk need a specific assessment. [1]
What comes next?
Clarify why the test was ordered and what would follow from each possible result. Persistent bloating, pelvic discomfort, or other new symptoms should be assessed on their own merits rather than dismissed because CA 125 is normal. [1]
Are we following a known condition or assessing a specific finding, and how does imaging fit with this result?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
