What is the CA-125 blood test?

A CA-125 test is a blood test that measures the amount of the protein CA-125, also called cancer antigen 125, in a person’s body.

CA-125 is a type of biomarker, or a substance in the blood that may be a sign of a condition or disease. A high level of CA-125 can be a sign of cancer, particularly ovarian cancer.

However, the test can have both false positive and false negative findings. CA-125 levels can be normal even if a person has cancer, or they can be elevated in a patient who does not have cancer. For this reason, a CA-125 test is not an effective screening for ovarian cancer.

Sometimes, physicians will order a CA-125 test as part of an overall approach to monitoring certain types of cancer – especially during and after treatment for the disease.

It also can be helpful in the early detection of ovarian cancer in women who are at increased risk of getting the disease. This could include factors such as if an immediate family member had ovarian cancer, or if the woman had ovarian cancer in the past.

However, a CA-125 test is rarely useful for women with no symptoms and no risk factors.

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