CA 125 blood test
Cancer antigen 125
In short
A typical adult CA 125 result is under 35 U/mL. A small rise is common before menopause, and most often comes from something other than cancer. When it is used to follow a known condition, the trend over repeat tests matters most. Always read your result against the range printed on your own report.
A protein made by the linings of the belly, chest and uterus.
CA 125 is mostly used to follow a known condition over time, most often ovarian cancer during and after treatment. It is not a good screening test for people at average risk, because many common things raise it. Periods, pregnancy and endometriosis (tissue like the uterus lining growing elsewhere) can all push it up.
Is my CA 125 high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults | under 35 | U/mL |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your CA 125 is high
A small rise is common before menopause, and most often comes from something other than cancer. When it is used to follow a known condition, the trend over repeat tests matters most.
Common reasons
- A menstrual period around the time of the test
- Endometriosis, a common cause of a raised CA 125
- Fibroids, harmless growths in the uterus
- Pregnancy, especially the first three months
- Pelvic inflammatory disease, an infection of the uterus, tubes or ovaries
- Liver disease, an inflamed pancreas, or fluid in the belly or chest
- Less often: ovarian or another cancer, or its return after treatment
What can throw it off
CA 125 can rise during a period, so where you are in your monthly cycle can change the result.
Questions to take to your appointment
- 1Is this test being used to follow something, or was it a one-off?
- 2Could my period, endometriosis or a pregnancy explain it?
- 3Should it be repeated at a different point in my cycle?
Read together with
Doctors rarely read CA 125 alone. These usually sit next to it.
Quick answers
What is the CA 125 blood test?
CA 125 (Cancer antigen 125): A protein made by the linings of the belly, chest and uterus. CA 125 is mostly used to follow a known condition over time, most often ovarian cancer during and after treatment. It is not a good screening test for people at average risk, because many common things raise it. Periods, pregnancy and endometriosis (tissue like the uterus lining growing elsewhere) can all push it up.
What is a normal CA 125 level?
For most adults, CA 125 is typically under 35 U/mL. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high CA 125 mean?
A small rise is common before menopause, and most often comes from something other than cancer. When it is used to follow a known condition, the trend over repeat tests matters most. Common reasons include a menstrual period around the time of the test; endometriosis, a common cause of a raised CA 125; fibroids, harmless growths in the uterus; and pregnancy, especially the first three months. A doctor reads it together with your other results and how you feel.
What can affect my CA 125 result?
CA 125 can rise during a period, so where you are in your monthly cycle can change the result.
What should I ask my doctor about my CA 125?
Questions worth taking to the appointment: Is this test being used to follow something, or was it a one-off? Could my period, endometriosis or a pregnancy explain it? Should it be repeated at a different point in my cycle?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- MedlinePlus — CA-125 blood test
- MedlinePlus — CA-125 blood test (ovarian cancer)
- ABIM — Laboratory test reference ranges (January 2026)
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.