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Should the CA 125 Test Be Used in General Practice?

“CA 125” is a glycoprotein that is associated with certain conditions, including inflammation and cancer. It is called “125” as this was the number of attempts before success in identifying an antibody on the surface of ovarian cancer cells. However, the antibody produced against CA 125 was subsequently found to be of little use. CA 125 is normally produced by ovarian cells, breast tissue, pancreatic cells, the peritoneum and the pleura. Therefore it is commonly raised in cases of ruptured ovarian cysts and ovarian cancer (but is not normally elevated in ovarian mucinous tumours), any cause of peritonitis, pancreatitis, recent abdominal or chest surgery, endometriosis, fibroids and ectopic pregnancy.

Its main use is serially, when used to track patients who have certain types of ovarian cancer. In these women, a significant change in the serum CA 125 level can indicate relapse or incomplete response to treatment. It is important to note that 1% of healthy women will normally have mildly elevated CA 125 levels.1 The higher the level, the more likely there is to be pathology present. However, because half of women with early ovarian cancer will have normal levels, testing of CA 125 levels is not suggested in asymptomatic women. 1,2 It may be used in addition to pelvic ultrasound to help diagnose ovarian cancer, if this is suspected.2

The summary why it is not suggested for use by General Practitioners is as follows:

“The test misses up to 50% of those with early ovarian cancer when treatment is most successful. Furthermore, the test is falsely elevated in a portion of the population due to conditions unrelated to cancer. CA 125 is especially unreliable in screening pre-menopausal women because both ovulation and menstruation can cause elevated levels.”1

“…CA 125 can be absent when disease is present, or levels can be high when no disease or no malignant disease exists. In addition, two patients with the same level can have widely different disease burdens.”1

“Currently there are no tests effective enough for a population based screening program for ovarian cancer. In addition, there is no evidence to suggest that screening will reduce the number of deaths from ovarian cancer.”2 

“Currently, there is no evidence that monitoring or screening leads to reduced mortality from ovarian cancer in women at increased risk. This is because there is currently no effective test for the early detection of ovarian cancer.”2


1. The Foundation for Women’s Cancer. Understanding  A 125 levels. 2011. Chicago [US]


2. Cancer Council Australia. Ovarian Cancer Fact Sheet, 2016 Apr