Frequently Asked Questions (FAQ) about the CA-125 Test

from OVARIAN PLUS INTERNATIONAL Newsletter


What is a CA-125 test?

CA-125 is a test done on a blood sample drawn in a laboratory. The assay (analysis) assesses the amount of an antibody that recognizes an antigen in tumor cells.

What does the test entail?

A blood sample is drawn, just as for a variety of other laboratory tests.

What are the statistics of its accuracy/inaccuracy?

Slightly over 80 percent of women who have ovarian cancer will have an elevated CA-125 in the liquid portion of their blood (serum) at the time of diagnosis. (True positive).

Three other scenarios that can occur with any lab test must be mentioned:

- False positive. The rate of "false positives" with CA-125 makes it inadequate for use BY ITSELF for screening of high-risk or healthy women; it should be supplemented with transvaginal sonography and a rectovaginal pelvic exam all done at the same time.

Premenopausal women are more likely than postmenopausal women to receive a "false positive" CA-125. This DOES NOT lead to unnecessary surgery if the physician is experienced in follow-up. The test should be repeated, more than once if necessary. If CA-125 continues to double outside a normal range, noninvasive tests in addition to those mentioned above should be conducted. Further follow-up, if needed, is suggested, short of surgery. (Surgery should never be done unless necessary in any situation.) For ongoing coverage of these issues, please see the OVARIAN PLUS INTERNATIONAL Newsletter.

-- False negative. In CA-125, the rate of "false negatives" also makes it important to use the test as part of a regimen that includes transvaginal sonography and rectovaginal pelvic exam.

-- True negative. As indicated above, repeating the test to observe a trend is an important new way of using CA-125. Consumers often have to ask their physician to arrange this.

What does it mean when it's elevated?

Especially in premenopausal women, elevated CA-125 can mean any of several benign conditions, or a "false positive," or ovarian cancer or another type of cancer.

What does it mean when it's NOT elevated?

A physician specifically experienced in the interpretation of CA-125 results can best assess this for the individual patient. However:

* The wise consumer has the test repeated several times if there is any doubt about her symptoms or diagnosis or risk factor (family history of ovarian cancer confers the highest possible risk known to date, and other factors elevate risk significantly.)

* If CA-125 is "negative" (not elevated) repeatedly, and no symptoms are present, and no significant risk factors exist (family history of ovarian, breast, endometrial or colorectal cancer; personal history of breast cancer; or took infertility drugs for a prolonged period and did not get pregnant-suspected risk factor)... and all other test results are normal... then the CA-125 result is more likely to be a "true negative."

* CAUTION! Almost 20 percent of women who have ovarian cancer do not ever have elevated CA-125. That is why it is ESSENTIAL to use CA-125 only as part of a diagnostic regiment that includes transvaginal sonography and a rectovaginal pelvic exam.

What's the difference between an CA-125 and CA-125II? Are they interchangeable?

CA125II is a new assay that has less variation from day to day. Since the original CA-125 ("first generation") test kits are no longer sold to laboratories, it is believed that few if any old plain CA-125 tests are being given in the United States as of November 1996.

** CA-125 and CA-125II ARE NOT INTERCHANGEABLE !

"The precise value obtained... may differ, but the trend using each assay over time should be quite similar." (OVARIAN PLUS INTERNATIONAL Newsletter, Summer 1996.)

Your CA-125II results may be several points higher than your old CA-125 result was.

What else should I know?

Insist that your health professional and laboratory provide you the following crucial information about your CA-125 test every time you have one done, in writing (and keep your test results on file indefinitely):

1.] The generation of the test (CA-125 II, or was it CA-125 first generation?).

2.} The name of the manufacturer of the assay (example: Abbott, or Centocor)

3.] The type of assay used (example: radioimmunoassay, sandwich method).

4.] Your result

NOTE: In the recent past, different manufacturers' assays sometimes provided different results...a potentially deadly problem identified in the medical literature.


Ovarian Plus International Newsletter is published by Ceil Sinnex, the world's first ovarian cancer advocate, fighting for our rights since 1990.

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