CA 125
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What is CA 125?
CA 125 is a protein that is a so-called
tumor marker or biomarker, which is a
substance that is found in greater concentration in tumor cells than in other
cells of the body. In particular, CA 125 is present in greater concentration in
ovarian cancer cells than in other cells. Its function is not currently
understood. CA stands for cancer antigen.
How is CA 125 measured?
CA 125 is usually measured from a blood sample. It can also be measured in
fluid from the chest or abdominal cavity. The tests currently in use are all
based upon the use of an antibody that is directed against the CA 125 protein
(monoclonal antibody technique).
In 1996, an improved version of the test was introduced and is sometimes
denoted as CA 125 - II. The numerical figure of the second generation test
results may be higher or lower than a first generation test. When comparing
multiple test results over time, it can be important to know which method was
used.
What is the normal range for CA 125?
The normal values for CA 125 may vary slightly among individual laboratories.
In most laboratories, the normal value is less than 35 U /ml.
Next: What does an elevated CA 125 mean and how is the test used? »
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