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What is a CA125 blood test?

CA125 is a protein that is found in blood.

A small sample of blood will be taken from your arm and sent to a lab where a simple test will measure the level of CA125 in your blood sample.


CA125 guide

You can also download this factsheet as a PDF to keep or print off.

In most healthy women the level of CA125 is usually less than 35. However, some women do have a naturally high level of CA125 in their blood.

The level of CA125 in the blood can rise for many reasons, which include endometriosis, menstruation, ovarian cysts, and sometimes ovarian cancer.

Your GP may advise you not to have the test immediately before, or during your period as is can interfere with the result.

Why has my GP asked me to have a CA125 blood test?

Symptoms including bloating, tummy pain, difficulty eating or feeling full and needing to wee more often or urgently can sometimes be caused by ovarian cancer.

It is very unlikely that you will have ovarian cancer, but your GP will want to rule out the possibility quickly. The CA125 test is a useful way for your GP to gather some more information and will help your GP decide what to do next. 

When do I receive the results?

Your GP will let you know how long your test result should take to come back from the lab. If you don’t hear anything within a couple of weeks, give your GP a call – sometimes results get lost.

If your test result is above 35, your GP will arrange further tests or a follow-up appointment.

Does a CA125 result above 35 mean I have ovarian cancer?

No. The level of CA125 in your blood can increase for other reasons, not just ovarian cancer. A CA125 blood test result above 35 is not in itself an ovarian cancer diagnosis.

If the level of CA125 in your blood is 35 or higher, your GP should arrange for you to have an ultrasound scan of your tummy and pelvis.  The ultrasound scans will create pictures of your ovaries so that they can be checked for anything unusual, and will help your GP to gather more information.

Read more about ultrasound scans.

Does a CA125 result below 35 mean that I don’t have ovarian cancer?

Most women with a result below 35 will not have ovarian cancer. However, a small number of women with ovarian cancer will have a CA125 test result below 35.

If your symptoms continue or worsen then you must go back to your GP and let them know, make an appointment for a check up within one month.

Try keeping a symptoms diary: each day make a quick note of each symptom and also how bad it is. This might help your GP identify the cause of your symptoms.

For more information on how to make the most of your GP appointment, see our top tips.

If you have further questions after reading this information, please speak to your GP.

Download our CA125 factsheet

Download our CA125 factsheet as a PDF to keep or print off.


Find out more 


The information on this page is approved by the Information Standard scheme to ensure that it provides accurate and high-quality information.


Last reviewed: January 2015
Next review: 2017