CA-125 Blood Test

The CA-125 blood test measures the level of a protein produced by ovarian cancer cells. The protein, CA-125, is known as a tumor marker because it is usually present at higher levels in women with ovarian cancer. CA-125 is most reliable, and most commonly used, to detect recurrent ovarian cancer in women who have been previously treated. If the CA-125 level is high before treatment, it can also be used to monitor or assess the effectiveness of chemotherapy treatment in women with ovarian cancer. Doctors generally look at the trend in the CA-125 levels over a course of time, rather than at each individual CA-125 level. These levels can help predict treatment outcomes for not only ovarian cancer but also closely related cancers such as fallopian tube cancer and primary peritoneal cancer.

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Although CA-125 testing is helpful for monitoring treatment, this test alone cannot diagnose ovarian cancer, nor is it effective in screening healthy women for ovarian cancer. A high level of CA-125 does not necessarily mean you have ovarian cancer; other noncancerous conditions such as inflammatory conditions of the abdomen, recent surgery, and gynecologic conditions like fibroids, endometriosis, ectopic pregnancy, or a ruptured cyst can all cause an increase in CA-125. At the same time, a low level of CA-125 does not mean you are cancer free; not all ovarian cancer cell types produce CA-125, and some produce only low levels.