Screening & Gynecologic Cancer
CA-125 Blood Test: What High Levels Mean and When It's Used
CA-125 is a blood test for a protein made by many ovarian cancer cells, but also by plenty of normal and benign tissues. It's used mainly to help evaluate a pelvic or ovarian mass and to track ovarian cancer during and after treatment. It is not a screening test for people without symptoms, because lots of non-cancer conditions raise it and it can be normal in early cancer.
Most people land on this page in one of two moods: worried about a number that just came back high, or wondering whether to ask for the test "just to check." This guide covers both.
What is CA-125?
CA-125 stands for cancer antigen 125. It's a protein on the surface of many cells, including cells lining the abdomen, chest, uterus and fallopian tubes. Many ovarian cancers release large amounts of it into the blood.
It's one of several tumor markers: substances that can run higher in some cancers. Tumor markers are rarely enough to diagnose cancer on their own.
What is a normal CA-125 level?
Many labs use 35 units/mL as the upper limit of normal. Ranges vary by lab and test method, so compare your result with the range printed on your report.
Three things to hold onto:
- Above 35 doesn't mean cancer. Many benign conditions raise CA-125, especially before menopause.
- Normal doesn't rule out cancer. CA-125 is normal in about half of early-stage ovarian cancers.
- Trends matter more than one number. Doctors often watch whether CA-125 is rising, falling or holding steady.
What raises CA-125 besides cancer?
| Benign causes | Cancer-related causes |
|---|---|
| Endometriosis | Ovarian, fallopian tube or peritoneal cancer |
| Fibroids and adenomyosis | Endometrial cancer |
| Menstruation | Pancreatic, breast, lung or colon cancer (sometimes) |
| Pregnancy | |
| Pelvic inflammatory disease | |
| Benign ovarian cysts | |
| Liver disease, including cirrhosis | |
| Heart failure or fluid around the lungs or belly | |
| Recent abdominal surgery |
Because so many benign causes are tied to hormones and the menstrual cycle, an elevated CA-125 is more concerning after menopause than before. A 34-year-old with known endometriosis and a mildly high CA-125 is in a very different situation from someone who is postmenopausal with a new mass.
"Can I just get tested to be safe?"
You can ask, and many people do, especially after a friend's or relative's diagnosis. Most clinicians won't order it for peace of mind if you have no symptoms and average risk. Here's why.
Large studies tested yearly CA-125 plus transvaginal ultrasound as screening for people at average risk. They found:
- No reduction in deaths from ovarian cancer
- Many false positives, leading to unnecessary surgery
- Serious complications in some people who had surgery for what turned out to be benign findings
Based on this, the USPSTF recommends against routine ovarian cancer screening in people at average risk with no symptoms, and ACOG agrees. A high result from a benign cause can mean more scans, weeks of worry and sometimes surgery you didn't need. A normal result can give false reassurance.
A better first step: talk through your symptoms and your family history. If ovarian, breast, colon or uterine cancer runs in your family, ask about genetic counseling. That conversation tells you far more than a single blood test. See BRCA genetic testing.
When CA-125 actually helps
Evaluating a pelvic or ovarian mass
If an ultrasound shows a mass on the ovary, CA-125 helps estimate the chance it's cancer. ACOG guidelines use it together with menopausal status, ultrasound features and other findings to decide whether to refer to a gynecologic oncologist. Sometimes it's combined with other blood tests, such as HE4, in risk calculators. Ask which ones were used.
Monitoring ovarian cancer
For people diagnosed with ovarian cancer, CA-125 is often checked:
- Before treatment to set a baseline
- During chemotherapy to see if treatment is working
- After treatment to watch for recurrence
A falling CA-125 usually means treatment is working. A rising level may lead to more imaging. Many patients say the wait for these results is one of the more stressful parts of follow-up; it's fine to ask your team how and when you'll hear.
People at high risk
For people with BRCA variants or Lynch syndrome who haven't had risk-reducing surgery yet, some clinicians use CA-125 with ultrasound as surveillance. It hasn't been shown to reduce deaths and is not a replacement for risk-reducing surgery.
Persistent symptoms
If you have ongoing bloating, pelvic pain or feel full quickly, your clinician may order CA-125 with a pelvic ultrasound. Here it's part of a diagnostic workup, not screening. More on which symptoms count in ovarian cancer symptoms.
What the test is like
It's a simple blood draw, usually with no fasting. Some clinicians prefer to avoid testing during your period, because menstruation can nudge the level up slightly. If you have a choice of dates, mention where you are in your cycle. Results typically come back within a few days, and they often hit the patient portal before your clinician has a chance to call. If you see a flagged number, don't panic-read; send a portal message asking when you can talk it through.
Your CA-125 is high. What happens next?
Next steps depend on your age, symptoms and other results. They may include:
- Repeat CA-125 in several weeks, especially before menopause
- Transvaginal ultrasound if not already done
- CT or MRI if there's concern for spread
- Referral to a gynecologic oncologist if a mass looks suspicious
If you're referred, it's not a diagnosis. It means a specialist will look at the full picture. Studies support having surgery for suspected ovarian cancer done by a gynecologic oncologist, and New York City has several NCI-designated cancer centers along with gynecologic oncologists at community hospitals across Long Island and the Hudson Valley. You can browse gynecologic oncologists in Manhattan or anywhere in the state.
Questions to bring to your appointment
- Why was this test ordered for me?
- What's the normal range at this lab?
- Could my period, endometriosis or fibroids explain the result?
- Do I need a repeat test, and when?
- Do I need an ultrasound or other imaging?
- Should I see a gynecologic oncologist?
Write them down before you go. These visits move fast, and it's easy to blank.
When to see a doctor
Make an appointment if you have:
- Bloating, pelvic or belly pain, trouble eating or urinary urgency almost every day for more than 2 to 3 weeks
- A known ovarian cyst with new or worsening pain
- An elevated CA-125 result you don't understand
- A family history of ovarian or breast cancer and new symptoms
Seek urgent care for sudden, severe pelvic pain, fever with pelvic pain, or a rapidly swelling belly.
Search our directory for a gynecologist or gynecologic oncologist across New York City, Long Island and the Hudson Valley.
Frequently asked questions
What is a CA-125 test?
CA-125 is a blood test that measures a protein made by some ovarian cancer cells and by many normal tissues. It is mainly used to evaluate a pelvic mass and to monitor ovarian cancer treatment.
What is a normal CA-125 level?
Many labs use 35 units/mL as the upper limit of normal, but ranges vary by lab. A result above that does not mean cancer, and a normal result does not rule it out.
Can CA-125 be used to screen for ovarian cancer?
No. The USPSTF recommends against ovarian cancer screening, including CA-125, for people at average risk without symptoms because it has not been shown to save lives.
What else can cause a high CA-125?
Endometriosis, fibroids, menstruation, pregnancy, pelvic infection, liver disease and other conditions can raise CA-125, especially before menopause.
Should I ask for a CA-125 test?
If you have persistent symptoms such as bloating or pelvic pain, talk with your clinician. They will decide whether a CA-125 test and a pelvic ultrasound make sense.
Sources
- National Cancer Institute — Tumor Markers in Common Use
- USPSTF — Ovarian Cancer: Screening (2018)
- ACOG — Evaluation and Management of Adnexal Masses (Practice Bulletin 174)
- MedlinePlus — CA-125 Blood Test
- American Cancer Society — Tests for Ovarian Cancer
This article is for general education and is not medical advice. It does not replace an evaluation by a licensed clinician who knows your history. If you think you have a medical emergency, call 911.