CA 125

CA 125 is a tumour marker measured in blood, primarily to monitor treatment in women with diagnosed ovarian cancer and as part of a doctor-led investigation when the disease is suspected. It is not a test for early cancer detection in healthy women: it is also raised in many benign conditions and is often normal in early ovarian cancer.

Who the test is for

• women with diagnosed ovarian cancer, before treatment, as a baseline value,
• women being treated for ovarian cancer, to monitor response to chemotherapy or surgery,
• women after completing ovarian cancer treatment, if the oncologist decides to monitor CA 125,
• women with persistent or frequently recurring symptoms such as abdominal bloating, feeling full early, abdominal or pelvic pain, and more frequent or urgent urination, particularly after age 50,
• women with an ovarian cyst or mass detected on ultrasound.

What CA 125 is and what it shows

CA 125 (English: cancer antigen 125) is a protein produced by cells lining the abdominal and chest cavities and by the lining of the uterus and fallopian tubes. There is normally little in the blood. It rises when those linings are irritated or inflamed, in some benign gynaecological conditions and in most advanced ovarian cancers.

CA 125 alone therefore neither establishes nor excludes cancer. It is useful when a doctor interprets it alongside examination, ultrasound and other findings, with changes over time being most informative.

For symptoms suggestive of ovarian cancer, a doctor may refer for CA 125 and ultrasound; with an ovarian cyst or mass, CA 125 is considered alongside the ultrasound findings and menopausal status. Read more about these symptoms in the article Early signs of ovarian cancer.

CA 125 is not recommended for early ovarian cancer detection in asymptomatic women, and Croatia has no national screening programme for this disease. Women with a marked inherited risk, such as a BRCA1 or BRCA2 gene change, agree a monitoring plan with a gynaecologist and geneticist.

Preparation and sample

CA 125 is measured in venous blood and fasting is not required. If you are menstruating, blood collection is best after your period ends unless a doctor says otherwise, because CA 125 can be raised during menstruation. Pregnancy and recent abdominal surgery or inflammation can raise CA 125 and are considered when interpreting results.

If CA 125 is monitored over time, it is best to use the same laboratory because results from different methods are not always directly comparable.

How to interpret a CA 125 result

For most methods, the upper limit is 35 U/mL (the same as kU/L); the reference interval printed on your report applies. Results are interpreted alongside symptoms, age, menopause and ultrasound findings.

Raised CA 125

Raised CA 125 does not mean you have cancer. Common benign causes include:

• menstruation, pregnancy, endometriosis, uterine fibroids, ovarian cysts and pelvic inflammatory disease;
• liver disease, particularly cirrhosis, and fluid in the abdomen or around the lungs;
• pancreatitis, kidney or heart failure, peritonitis and the period after abdominal surgery;
• some autoimmune diseases, such as lupus.

CA 125 may also be raised in other malignancies, such as endometrial, pancreatic, lung, breast and colorectal cancer, and lymphoma. False-positive elevated results are more common before menopause because benign gynaecological conditions are also more common. After menopause, raised CA 125 requires more careful investigation, usually pelvic ultrasound.

Normal CA 125

A normal result does not rule out ovarian cancer: approximately half of women with early-stage ovarian cancer have CA 125 within the reference interval. If symptoms persist, see a doctor even if the result is normal.

CA 125 during and after treatment

A fall during treatment usually means the disease is responding to therapy. A normal value after treatment does not guarantee cure, and a rise on follow-up is not in itself proof of recurrence: it may indicate residual or recurrent disease, but also inflammation or another benign cause. A rise is therefore confirmed by repeat measurement, and an oncologist decides on further investigation.

CA 125 alone or with other markers

A doctor sometimes requests other markers alongside CA 125, such as HE4 when assessing an ovarian mass, or CEA and CA 19-9 when distinguishing an ovarian tumour from a gastrointestinal tumour. We explain what tumour markers can and cannot do in the article Tumour markers.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list. If a doctor has recommended several markers, the Women’s marker panel includes CEA, CA 19-9, CA 125 and CA 15-3.

Frequently asked questions

What does CA 125 above 35, 50 or 200 mean?

A value above 35 U/mL means CA 125 is raised, but does not explain why. The higher the value, the more further investigation is needed, but levels of several hundred can also occur in benign conditions, such as liver cirrhosis with abdominal fluid or peritonitis. Its meaning can only be assessed alongside gynaecological examination and ultrasound.

Can CA 125 be raised because of endometriosis or fibroids?

Yes. Endometriosis, particularly advanced disease, and uterine fibroids are common benign causes of raised CA 125 in premenopausal women. Whether further investigation is needed is assessed alongside gynaecological examination and ultrasound.

Should CA 125 be measured preventively?

Not in women without symptoms or high inherited risk, because it often gives falsely elevated results while early disease may be missed. If bloating, abdominal or pelvic pain or feeling full early persists for several weeks, see a doctor who will decide on tests.