All Checked Up
March 30, 2026
In this article we will look at Cancer Antigen 125 (CA 125), how it is used in detecting Ovarian Cancer and some other cancers and non-cancerous conditions, how accurate it is in detecting Ovarian Cancer when you should get a CA125 test, and what the NICE guidelines are for interpreting CA125 test results.
Cancer Antigen 125 (CA 125) belongs to the mucin family glycoproteins. A glycoprotein is a molecule that is a combination of a carbohydrate (or glycan) linked to protein. CA125 is secreted into the bloodstream by both normal and cancerous cells. It is normal to have some CA 125 in the blood, but levels may be higher in Ovarian Cancer and some other cancers. This is because CA125 can be found on the surface of most ovarian cancer cells.
However, CA 125 levels may also be high in other types of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease. CA 125 levels may also be raised in other cancers.
Levels of CA125 in the bloodstream can be quantitatively measured through a simple blood test. You can have blood taken from a vein in your arm by a Phlebotomist at our clinic in Cheshire or London, or you can order a self-collection kit to collect a finger prick blood sample at home and send it off to our lab for an accurate quantitative result.
It is estimated elevated CA125 levels have been found in about 80% of women with ovarian cancer.
A recent study funded by Cancer Research UK and NIHR found that the CA125 blood test detected more than 77% of all ovarian cancers and more than 85% of invasive ovarian cancers which are most likely to be fatal.
Crucially, the study also found more than 38% of ovarian cancers were picked up early (at either stage I or II) when treatment is most likely to be successful.
It also noted that the CA125 blood test was able to pick up other cancers including lung, pancreatic, or bowel cancer. All in all, 1 in 3 women aged over 50 years old who had a CA125 blood test result above the NICE recommended cut-off value of 35 KIU/L were diagnosed with some form of cancer.
The study was conducted by scientists at the Universities of Cambridge, Manchester, and Exeter and looked at more than 50,000 symptomatic women who had a CA125 blood test at their GP surgery between 2011 and 2014. Symptoms included abdominal pain or bloating, or a change of bowel habits.
Ovarian cancer is cancer that starts in the ovaries. There are different types of ovarian cancer depending on the type of cell the cancer starts in. Abnormal cells can begin to grow and divide in an uncontrolled way which can lead to a tumour. Early detection is key, as these cancer cells can gradually move into the surrounding tissues and other areas of the body.
Ovarian cancer is the sixth most common cancer in women. In 2016–2018, there were approximately 7500 new cases diagnosed, equating to about 21 cases daily and around 4100 deaths from ovarian cancer, accounting for 5% of all cancer-related deaths in women.
It is estimated that 1 in 50 UK females will be diagnosed with ovarian cancer in their lifetime. Worldwide in 2020, it was estimated that there were approximately 314,000 new cases of ovarian cancer and 207,250 deaths from ovarian cancer
UK government NICE guidelines recommend a CA 125 test for women aged 50 years or over who report one or more symptoms occurring persistently (over a month) or frequently (more than 12 times a month) that suggest ovarian cancer. These symptoms include:
feeling ‘bloated’, loss of appetite or feeling full quickly, pain in the abdomen or pelvic area, needing to pass urine urgently or more often than usual, and unexplained tiredness, weight loss or changes in bowel habit (for example, constipation or diarrhoea)
A CA 125 test is sometimes used to screen women who are at high-risk because they have a family history of ovarian cancer or women who have the BRCA1 or BRCA2 gene mutation.
A normal CA125 level in the blood is less than 35 IU/mL. CA 125 levels of 35 IU /mL or above are considered abnormal and elevated but does not mean you have ovarian cancer. Usually, a CA 125 test is used in combination with other tests, such as an Ultrasound scan as well as an abdominal and pelvic examination by your Doctor
Watch this short video from Target Ovarian Cancer about the CA125 blood test
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