CA-125 Test
Overview
The CA-125 blood test measures the level of cancer antigen 125 in the bloodstream. This protein, also known as CA-125, is a type of tumor marker and may be higher in certain health conditions. Doctors often use the CA-125 test to check on patients undergoing treatment for cancers such as ovarian, endometrial, peritoneal, or fallopian tube cancer.
| Test Name | Main Protein Measured | Used for Monitoring | Other Tumor Markers |
|---|---|---|---|
| CA-125 blood test | Cancer antigen 125 | Ovarian and related cancers | HE4 |
However, some benign (non-cancerous) issues—like menstruation or uterine fibroids—can also cause high CA-125 levels. Doctors do not recommend routine screening for ovarian cancer with the CA-125 test.
Reasons for Use
Doctors often use a CA-125 blood test to help manage and monitor certain health conditions, especially cancers of the female reproductive organs. It plays an important role in tracking how well treatment is working and detecting whether the disease returns.
Another reason for this test is to check for ovarian cancer in people at high risk. Factors that increase risk include a family history of ovarian cancer, BRCA1 or BRCA2 gene mutations, or a genetic syndrome linked to a higher cancer risk. For those at very high risk, doctors might combine a CA-125 test with a transvaginal ultrasound every 6 to 12 months.
Main Uses
| Use Case | Details |
|---|---|
| Monitoring cancer treatment. | Tracks CA 125 to check response to therapy in ovarian and related cancers. |
| Screening for high-risk individuals. | Used for those with strong family or genetic risk, often along with ultrasound. |
| Detecting cancer recurrence. | Rising CA 125 levels can signal a cancer’s return. |
Doctors do not recommend this test as a routine screening tool for healthy women without risk factors. Not everyone with ovarian cancer shows high CA-125 levels, and benign conditions—such as endometriosis, abdominal pain, bloating, pelvic pain, or abdominal distention—can also raise CA-125.
Providers interpret the results of a CA-125 test alongside other tests, such as pelvic imaging or the Risk of Ovarian Cancer Algorithm (ROCA), to make a clinical decision. Further exams might include serum human epididymis protein 4 (HE4), CT scans, or MRI, especially when symptoms of ovarian cancer—like bloating or ongoing abdominal discomfort—are present.
This test can lead to unnecessary worry or procedures when used without clear cancer risk. Providers should use it as part of a broader diagnostic approach, especially for those with symptoms or a family history suggesting an increased chance of ovarian cancer.
Possible Complications
A blood draw for a CA 125 test carries minimal risk. Some people might notice slight bleeding, develop a small bruise, or feel a bit dizzy after the procedure. In rare cases, infection can occur. NCCN guidelines note that complications from the test are uncommon.
How You Get Ready
No special steps are necessary before a CA 125 blood sample. People can eat or drink normally before the test if it is done only for CA 125. There are no dietary or activity restrictions. The process is simple and does not require extra preparation.
What You Can Expect
A healthcare worker will take a blood sample, usually from a vein in the arm or hand. The process is simple and quick. Most people can go back to their day right after the test.
Test Process
- A healthcare provider draws blood with a needle.
- The lab analyzes the sample using an immunoassay like electrochemiluminescence testing.
- No downtime is needed.
Doctors may order typical exams for ovarian or pelvic issues—such as a pelvic exam, transvaginal ultrasound, or evaluation for pelvic masses or ovarian tumors—separately. This blood test does not involve imaging of the fallopian tubes or uterus.
Test Findings
The CA-125 test measures how much cancer antigen 125 is present in the blood. The usual reference range for CA-125 is 0 to 35 U/mL. Results above this range indicate elevated levels and could result from a variety of reasons.
Not all high CA-125 levels mean ovarian cancer; non-cancerous conditions like endometriosis, liver disease, menstruation, pelvic inflammatory disease, pregnancy, or uterine fibroids can also increase CA-125.
| CA-125 Level (U/mL) | Likely Interpretation |
|---|---|
| 0–35 | Within normal reference range |
| Above 35 | Elevated; further tests needed |
When healthcare providers monitor ovarian, endometrial, peritoneal, or fallopian tube cancer, falling CA-125 levels usually indicate a positive response to treatment. Rising levels can signal recurrent disease or continued cancer growth.
The accuracy of the CA-125 test depends on its sensitivity (how well it detects disease) and specificity (how well it avoids false positives). Tools like the Risk of Ovarian Malignancy Algorithm (ROMA) may also improve assessment.
