Healthy Body

Understanding the CA 125 blood test for ovarian cancer

Emma Harpham, Editor  |   14 Jun 2024

Navigating women’s health screenings can feel really daunting at times. We truly know first-hand how much of a toll it can take. If you’re there right now, we see you and we’ve got you.

Assessments like the CA 125 blood test for ovarian cancer are really important as part of understanding the bigger picture of your health, and getting in the know is key to feeling empowered and clued up during the process.

We’ve put together this at-a-glance guide to walk you through everything you need to know about the CA 125 blood test – including what it measures, when you might need it, and what the results actually mean.

Let’s get informed, together.

What is the CA 125 blood test?

The CA 125 blood test measures the amount of cancer antigen 125 in your blood. CA 125 is a protein that can be found on the surface of ovarian cancer cells. 

This test is frequently used in the monitoring and management of ovarian cancer – but isn’t a standalone diagnostic tool for the condition.

What is the CA 125 ovarian cancer link?

CA 125 is a protein biomarker associated with ovarian cancer

CA 125 is often present at higher levels in ovarian cancer cells, particularly in more advanced stages of ovarian cancer, than in normal healthy cells. 

When these cancerous cells shed CA 125 into the bloodstream, it results in elevated levels that can be detected through the blood test.

When might I need a CA 125 blood test

When might I need a CA 125 blood test?

Your GP might refer you to have a CA125 blood test, if;

  • You have symptoms of ovarian cancer – these can include persistent bloating, pelvic pain, and feeling full very quickly after eating 
  • You’re currently having or have finished having ovarian cancer treatment – this is to check the effectiveness of treatment
  • You have a family history of ovarian cancer – as part of a broader strategy to keep an eye on your ovarian health, if you’re thought to be at risk 

If your GP suggests this test, it might feel scary, but it’s part of their effort to get a clearer picture of what’s going on in your body.

How long for results of CA 125 blood test to come back, typically?

CA 125 test results should take a few working days to come back. They could take up to a week at busy times, and the exact timing can vary depending on the lab too.

If you don’t hear anything within two weeks, give your GP a call. 

What is a normal CA 125 level?

Typically, a CA 125 level below 35 units per milliliter (U/mL) is considered normal.

CA 125 levels can be normal even if you have cancer, so if you’re experiencing ovarian cancer symptoms, your doctor will usually ask for more testing.

What CA 125 levels indicate ovarian cancer?

CA 125 levels over 35 U/mL may indicate the presence of ovarian cancer, or other conditions. However, it is important to note that not all women with high CA 125 levels have cancer.

If you have a high CA 125 level and have symptoms of ovarian cancer, you will usually be referred for a transvaginal ultrasound, an MRI scan, or other further testing. You might repeat the test later on, to see if your levels have increased over time.

What CA 125 levels indicate ovarian cancer

How reliable is the CA 125 blood test for ovarian cancer?

Whilst being a helpful indicator for ovarian cancer, particularly in postmenopausal women over the age of 50 – the CA 125 blood test isn’t accurate enough to use as a diagnostic tool for ovarian cancer alone.

This said, research from 2020 from several UK universities found that it could be far more predictive than originally thought, and could even potentially pick up other forms of gynecological cancer as well.

However, several non-cancerous conditions can also lead to elevated CA 125 levels, especially in younger women.

Can ovarian cysts cause elevated CA 125?

Ovarian cysts, as well as uterine fibroids, could contribute to elevated CA 125 levels.

An ovarian cyst is a fluid-filled sac that develops on your ovary. They’re very common and usually resolve on their own – have a look at our guide to ovarian cyst symptoms and questions to ask during diagnosis, for more.

Can endometriosis cause elevated CA 125?

In a word – yes. CA 125 levels have been found to be significantly higher in women with moderate or severe endometriosis, and some research suggests it could be an important predictor of endometriosis in women of all ages.

The gold standard for diagnosing endometriosis though, is still laparoscopy, although the ReceptivaDx test – a groundbreaking test which looks for another protein biomarker associated with inflammation called BCL6 – is making leaps and bounds in detecting endometriosis and silent endometriosis in women, sooner.

What about my CA 125 level during menstruation?

It is thought that having your period could temporarily raise CA 125 levels in some individuals.

So if you’re premenopausal, it might be worth noting whether you’re on your period or not, if you’re being tested for CA 125.

The bottom line

Testing positive for elevated CA 125 levels does not necessarily mean that you have ovarian cancer. The test is just one piece of the puzzle in understanding your ovarian health.

The key takeaway here is to keep up open communication with your GP or doctor. They are there to guide you through the process, answer your questions, and help you understand what your test results mean in the context of your overall health.

Want to hear more from TRB? Read this next: Cancer and fertility – from preservation to chemo, let’s get the very latest

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