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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 factsheet preview

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 units per millilitre (u/ml). However, some women do have a naturally high level of CA125 in their blood.

As well as helping diagnose ovarian cancer, CA125 blood tests are sometimes used to monitor the treatment of ovarian cancer or check for signs of recurrence. For more information about this use of a CA125 blood test, please contact our Support Line

When should I request a CA125 blood test?

Symptoms including persistent bloating, feeling full quickly and/or loss of appetite, pelvic or abdominal pain and needing to wee more often or urgently than usual are sometimes caused by ovarian cancer.

If you have one or more of these symptoms frequently and persistently it is unlikely that you will have ovarian cancer, but your GP will want to rule out the possibility. The CA125 blood tests is a useful way to gather some more information and will help your GP decide what to do next. 

If you are concerned that you have these symptoms, ask your GP about ovarian cancer and having a CA125 blood test. 

How should I prepare for a CA125 blood test?

Your GP may suggest that you do not have the test if you are on your period as it may affect the result. If your blood is only being tested for CA125, you can eat and drink normally before the test and resume your normal activity straight afterwards.

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

No. The level of CA125 in your blood can rise for many reasons including endometriosis, menstruation, ovarian cysts, and sometimes ovarian cancer. This is one reason why it cannot accurately be used as a screening test for ovarian cancer. 

If the level of CA125 in your blood is 35 u/ml or higher, your GP should arrange for you to have an ultrasound scan of your tummy and pelvis. The ultrasound scan will create pictures of your ovaries so that they can be checked for anything unusual, and will help your GP to gather more information. In some areas of the UK, a CA125 blood test and ultrasound scan will be ordered at the same time. 

Read more about ultrasound scans.

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

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

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

Next steps

How do I get my test result?

Your GP will let you know how long your test result should take to come back from the lab, and they will also tell you how to find out the result of your test. However, if you don't hear anything within two weeks, give your GP a call - sometimes results get lost. If you have received your test results and you are not sure what they mean, go back to your GP and ask for clarification.

If your test result is about 35 u/ml your GP will arrange further tests or a follow-up appointment. 

What if my symptoms persist?

If your CA125 level is below 35 u/ml, but your symptoms continue or worsen then you must go back to tell your GP within a month. Why not keep a symptoms diary? Make a quick note every day of each symptom and how bad it is. This might help your GP to identify the cause of your symptoms. 

For more information on how to make the most of your GP appointment, see our 10 Top Tips.

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

Download our CA125 factsheet

Download our CA125 blood test fact sheet 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: June 2017
Next review: May 2020