CA 125 test
Medically reviewed on February 6, 2018
A CA 125 test measures the amount of the protein CA 125 (cancer antigen 125) in your blood.
A CA 125 test may be used to monitor certain cancers during and after treatment. In some cases, a CA 125 test may be used to look for early signs of ovarian cancer in women with a very high risk of the disease.
A CA 125 test isn't accurate enough to use for ovarian cancer screening in all women because many noncancerous conditions can increase the CA 125 level.
Many different conditions can cause an increase in CA 125, including normal conditions, such as menstruation, and noncancerous conditions, such as uterine fibroids. Certain cancers may also cause an increased level of CA 125, including ovarian, endometrial, peritoneal and fallopian tube cancers.
Why it's done
You may have a CA 125 test for several reasons:
To monitor cancer treatment. If you have ovarian, endometrial, peritoneal or fallopian tube cancer, your doctor may recommend a CA 125 test on a regular basis to monitor your condition and treatment.
But such monitoring hasn't been shown to improve the outcome for women with ovarian cancer, and it might lead to additional and unnecessary rounds of chemotherapy or other treatments.
To screen for ovarian cancer if you're at high risk. If you have a strong family history of ovarian cancer or you have the BRCA1 or BRCA2 gene mutation, your doctor may recommend a CA 125 test as one way to screen for ovarian cancer.
Some doctors may recommend CA 125 testing combined with transvaginal ultrasound every six months for women at very high risk.
However, some women with ovarian cancer may not have an increased CA 125 level. And no evidence shows that screening women with CA 125 decreases the chance of dying of ovarian cancer. An elevated level of CA 125 could prompt your doctor to put you through unnecessary and possibly harmful tests.
- To check for cancer recurrence. Rising CA 125 levels may indicate that ovarian cancer has come back after treatment. Regular monitoring of CA 125 has not been shown to improve outcomes for women with ovarian cancer and may lead to additional and unnecessary rounds of chemotherapy or other treatments.
If your doctor suspects you may have ovarian cancer or another type of cancer, he or she may recommend a biopsy to collect a sample of cells. Other tests that may be helpful in evaluating these cancers include a transvaginal or pelvic ultrasound and computerized tomography (CT).
How you prepare
If your blood is being tested only for CA 125, you can eat and drink normally before the test.
What you can expect
For a CA 125 test, a member of your health care team takes a sample of blood by inserting a needle into a vein, usually in your hand or arm. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.
Results of the CA 125 test are measured in units per milliliter (U/mL). The normal value is less than 35 U/mL.
If your CA 125 level is higher than normal, you may have a benign condition, or the test result could mean that you have ovarian, endometrial, peritoneal or fallopian tube cancer. Your doctor may recommend other tests and procedures to determine your diagnosis.
If you've been diagnosed with ovarian, endometrial, peritoneal or fallopian tube cancer, a decreasing CA 125 level often indicates that the cancer is responding to treatment. A rising CA 125 level may indicate a return or continued growth of the cancer.
A number of normal and noncancerous conditions can cause an elevated CA 125 level, including:
- Liver disease
- Pelvic inflammatory disease
- Uterine fibroids