CA125 blood test

Find out what the CA125 blood test is, when you might have one and what the results can tell you.

Find out what a CA125 blood test is, how it's used in diagnosing or ruling out ovarian cancer and what the results may mean. If you have a question that isn't covered here, please feel free to call our support line on 020 7923 5475 or speak to your GP.

What is a CA125 blood test?

CA125 is a protein that's 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.

A normal level of CA125 is usually less than 35 units per millilitre (u/ml). But 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 (the cancer returning).

For more information about this use of a CA125 blood test, you can speak to one of our nurse advisers by contacting our support line on 020 7923 5475.

When should I request a CA125 blood test?

Symptoms including persistent bloating, feeling full quickly and/or loss of appetite, pelvic or abdominal (tummy) 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's 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're 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 delay the test if you're 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. A CA125 blood test result above 35 u/ml isn't a diagnosis of ovarian cancer in itself. The level of CA125 in your blood can rise for many reasons including endometriosis, your period, ovarian cysts, and sometimes ovarian cancer. This is one reason why it can't 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. 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. 

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 won't have ovarian cancer. But a small number of women with ovarian cancer will have a CA125 test result below 35 u/ml.

If your symptoms continue or get worse 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. At many GP surgeries you can register for online access to your record and to see your results so ask your surgery for further information if this is how you'd like to access them. 

If you don’t hear anything within two weeks, give your GP a call. If you've received your test results and you're not sure what they mean contact your GP and ask them to explain.  

If your test result is above 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 get worse then you must go back to tell your GP within a month. Why not keep a symptoms diary [PDF]? 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 top tips.

If you have further questions after reading this information, please speak to your GP or call our support line on 020 7923 5475.

Last reviewed: August 2022

This information is reviewed regularly and is in line with accepted national and international guidelines. All of our publications undergo an expert peer review and are reviewed by women with ovarian cancer to ensure that we provide accurate and high-quality information. To find out more take a look at our information standards.