Cancer Antigen 125 (CA-125)
Cancer antigen 125 (CA-125) is a
protein found on the surface of many
ovarian cancer cells. It also can be found in other
cancers and in small amounts in normal tissue. A CA-125 test measures the
amount of this protein in the blood.
CA-125 is used as a tumor
marker, which means the test can help show if some types of cancer are present.
Most often, the CA-125 test is used to check how well treatment for ovarian
cancer is working or to see if ovarian cancer has returned.
Why It Is Done
The test for cancer antigen 125
(CA-125) is used to:
- Check to see if treatment for cancer is
working. If the level of CA-125 is going down, it usually means that the
treatment is working.
- Check to see if ovarian cancer has
- Check to see if the ovary is the main site of cancer in a
woman. If a doctor has found a cancer that has spread to another part of the
body (metastatic cancer), he or she may do a CA-125 test to find out where the
cancer started. High levels of CA-125 are a strong sign that the cancer started
in the ovary. But other types of cancer can increase CA-125 levels too.
The CA-125 test is not recommended as a screening test for
ovarian cancer at this time because it often has
false-positive results. But the CA-125 test and an
ultrasound scan may be used to test women who have a
high chance of developing ovarian cancer. Women have a high risk of getting ovarian cancer if they
have a family history of ovarian cancer or certain changes (mutations) in their
DNA (BRCA1 or BRCA2).
How To Prepare
You do not need to do anything before
you have this test.
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then put on a
How It Feels
The elastic band around your upper arm
may feel tight. You may feel nothing at all from the needle, or you may feel a
quick sting or pinch.
There is very small chance of problems from
having blood drawn from a vein.
- You may get a small bruise at the site. You
can lower your chance of bruising by putting pressure on the site for several
- In rare cases, the vein may become swollen after the blood
sample is taken. This condition is called phlebitis. You can use a warm
compress several times a day to treat this.
- Ongoing bleeding can be
a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can also make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your health professional before your blood is drawn.