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CA125 blood test

CA125 blood test

If you have any of the four main symptoms of ovarian cancer (persistent stomach pain, persistent bloating, needing to wee more frequently or urgently, difficulty eating or feeling full more quickly), your GP should refer you for a CA125 blood test to support their diagnosis.

What is a CA125 blood test?

CA125 is a protein that both women and men have in their blood. A high level of CA125 in your blood is a possible indicator of ovarian cancer, as CA125 can sometimes be produced by ovarian cancer cells. A CA125 blood test is used to check the level of the CA125 protein in the blood to support the diagnosis of a number of things including ovarian cancer. 

When might a CA125 blood test be necessary?

If your GP thinks your symptoms could be a sign of ovarian cancer, they'll recommend you have a blood test to check the level of a protein called CA125 in your blood. Your GP will undertake an examination of your tummy and/or internal vaginal examination before they make this referral. The CA125 test can either be carried out at your local doctor’s surgery, or you will be referred to your local hospital the same way you would for any other blood test. 

CA125 blood test results

The normal values for CA125 vary slightly among women, however a woman’s blood level of the CA125 protein will usually be less than 35 units per millilitre (U/mL). It is important to note that some women naturally have high levels in their blood and that an elevated level can also be a sign of:

  • Benign ovarian cysts
  • Chest infection
  • Endometriosis
  • Fibroids
  • Liver cirrhosis
  • Menstruation
  • Pancreatitis
  • Pelvic inflammatory disease
  • Pregnancy
  • Renal failure.

Having a raised level of CA125 is not a diagnosis of ovarian cancer, but it should lead to further investigations. These will usually be in the form of a referral for an ultrasound scan.

What if my CA125 blood test is normal?

If your CA125 blood test has come back normal it is unlikely that you have ovarian cancer. However, it is important to continue to monitor your symptoms as sometimes your CA125 levels can be normal in the early stages of ovarian cancer. If you've had a normal test result but your symptoms don't improve, go back to your GP as you may need to be re-tested.

Things other than ovarian cancer that could present with symptoms such as bloating, stomach pain, difficulty eating and weeing more frequently include:

  • Gallstones
  • Gastro infections
  • Indigestion
  • Irritable bowel syndrome (IBS)
  • Pulled muscles
  • Pregnancy
  • The onset of the menopause
  • Urinary tract infections.

Your GP should continue to investigate to see if your symptoms are linked to any of the above, or something else.

Reviewed: September 2022

Next review: September 2023