CA125 is a protein that's found in blood. Ovarian cancer, as well as other conditions, can sometimes raise the level of CA125 in your blood. A normal level of CA125 is usually less than 35 units per millilitre (u/ml).

During a CA125 blood test, a small sample of your blood will be taken and sent to a laboratory to measure the level of the CA125 protein.

As well as helping to diagnose or rule out 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 the CA125 blood test, speak to one of our nurse advisers by contacting our support line on 0808 802 6000 (freephone) or speak to your GP.

When should I request a CA125 blood test?

If you have symptoms of ovarian cancer, you should ask your GP about having a CA125 blood test. The CA125 blood test is a useful way to gather some more information and will help your GP decide what to do next. 

The main symptoms of ovarian cancer are:  

• persistent bloating (pooing more or less often than normal)    
• feeling full quickly and/or loss of appetite  
• pain in your tummy or pelvis (the area between your hip bones)  
• needing to wee more urgently or more often than usual. 

Sometimes there can be other symptoms:

• diarrhoea or constipation (a change in your bowel habit)  
• fatigue (feeling very tired)  
• losing weight without trying  
• unusual vaginal bleeding before the menopause or any vaginal bleeding after the menopause. 

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 raised CA125 level doesn’t mean you definitely have ovarian cancer. The level of CA125 in your blood can be high for other reasons, including conditions such as endometriosis, uterine fibroids, rheumatoid arthritis and ovarian cysts. Being on your period can also slightly raise the level. Some women have a naturally high level of CA125 in their blood.  

A CA125 test on its own isn’t enough to diagnose ovarian cancer. If your CA125 level is 35 units per millilitre (u/ml) or higher, your GP should arrange an ultrasound scan of your tummy and pelvis (the area between your hip bones). The scan will look at your ovaries so that they can be checked for anything unusual. An ultrasound scan is usually done on an urgent basis to rule out whether your symptoms and raised CA125 level could be due to ovarian cancer.  

Your GP may also ask for a repeat CA125 blood test. 

What if I have a CA125 result below 35 u/ml but I still have symptoms?

It is possible to have ovarian cancer with a CA125 test result below 35 u/ml.  

If you continue to have symptoms, you should go back to your GP within a month and ask whether you need an ultrasound scan. This is because sometimes ovarian cancer doesn’t cause a raised CA125 level and an ultrasound scan is needed to check the ovaries.

It’s helpful for your GP if you track and make a note of your symptoms. Download or order a symptoms diary for free.

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 laboratory, and they will also tell you how to find out the result of your test. You can register for online access to your medical record at your GP surgery. You can also do this on the NHS app. Ask your surgery if this is how you would like to access your results.   

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 continue?

If your CA125 level is below 35 u/ml, but your symptoms continue or get worse go back to your GP within a month. 

• Why not keep a symptoms diary? Make a quick note every day of each symptom. 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 for speaking to your GP.
• If you have further questions after reading this information, please speak to your GP or call our support line on 0808 802 6000 (freephone).