CA-125 blood test: normal range, high levels, endometriosis and ovarian cancer
CA-125 (CA-125) · Tumor marker (ordered alone, or with HE4 as the ROMA score) · reported in U/mL (equivalent to kU/L)
CA-125 (cancer antigen 125) is a protein found on the surface of cells that line the abdominal cavity, the chest cavity and the female reproductive tract, and a CA-125 blood test measures how much of it has leaked into the bloodstream. The normal range is under 35 U/mL. The test is best known as the ovarian cancer marker, because about 80 percent of advanced epithelial ovarian cancers raise it, and it is used to help assess a pelvic mass, to track how an ovarian cancer responds to treatment, and to watch for recurrence afterwards.
It is not a screening test for ovarian cancer, and it is not specific to it. Only around half of early-stage ovarian cancers raise CA-125, while a long list of common and harmless conditions do: menstruation, pregnancy, endometriosis, fibroids, ovarian cysts, pelvic infection, and anything that irritates the lining of the abdomen or chest, including liver disease with fluid, heart failure, pancreatitis and recent surgery. Two very large screening trials, one with over 200,000 women, found that routine CA-125 testing in women without symptoms did not reduce deaths from ovarian cancer.
Context decides what a high result means. In a premenopausal woman with a modest rise (35 to 100 U/mL) and no mass on ultrasound, endometriosis or a benign gynecological cause is far more likely than cancer. In a postmenopausal woman with an ovarian mass on ultrasound, any CA-125 above 35 U/mL changes the referral pathway, and values above 200 in any woman with a mass are treated as high-risk until proven otherwise. A single result is interpreted with the ultrasound, your age and your symptoms, never alone.
CA-125 at a glance
- What it is: a glycoprotein (MUC16) shed by the lining of the abdomen, chest and reproductive organs, and by most epithelial ovarian cancers.
- Normal: under 35 U/mL (some labs use 30 or 38). Units are U/mL, the same as kU/L. About 1 to 2 percent of healthy women are slightly above.
- Not a screening test: half of early ovarian cancers are missed, and most raised results in premenopausal women are benign (endometriosis, fibroids, cysts, periods, pregnancy, infection).
- With a pelvic mass: postmenopausal and above 35 U/mL, or premenopausal and above 200 U/mL, meets the US threshold for referral to a gynecologic oncologist.
- Main use: to follow known ovarian cancer, where a fall of 50 percent or more means treatment is working and a confirmed rise after remission usually comes 3 to 5 months before a scan shows relapse.
- Next step: a raised result is paired with a transvaginal ultrasound; if that is normal the test is repeated after your next period (or in 4 to 6 weeks) and benign causes are reviewed.
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What CA-125 measures
CA-125 is the shorthand for a very large sugar-coated protein, mucin 16, that coats the mesothelial cells lining the peritoneum, pleura and pericardium and the cells lining the fallopian tubes, uterus and cervix. These tissues shed a little of it into the blood all the time, and shed much more when they are inflamed, stretched or irritated, which is why fluid in the abdomen from any cause raises CA-125. Ovarian, fallopian tube and primary peritoneal cancers derived from this lining produce it in bulk.
The lab measures CA-125 with an immunoassay reported in units per millilitre (U/mL). Assays from different manufacturers are calibrated differently, so serial results used to follow a cancer should come from one laboratory. There is no need to fast. The protein clears with a half-life of about six days, so it takes several weeks for a level to fall after a cause is removed.
Because the test lacks both sensitivity and specificity on its own, it is combined with other information. The Risk of Malignancy Index multiplies the CA-125 value by scores for ultrasound features and menopausal status, with a result over 200 regarded as high risk. The ROMA score combines CA-125 with a second marker, HE4, and menopausal status to sort a pelvic mass into low or high risk. Neither replaces surgery and pathology for a diagnosis.
Normal range for CA-125
Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.
| Group | Typical range (U/mL (equivalent to kU/L)) | Notes |
|---|---|---|
| Adults, normal | Below 35 U/mL | Some labs use 30 or 38 U/mL. Levels fall slightly after menopause; the healthy postmenopausal median is around 10 to 15 U/mL. |
| During menstruation | May rise up to about 2-fold | Test in the first half of the cycle after bleeding stops, or repeat if the sample was taken during a period. |
| First trimester of pregnancy | Commonly 35–65 U/mL, occasionally higher | Settles after the first trimester; rises again briefly after delivery. |
| Endometriosis | Typically 35–100 U/mL | Deep disease or endometriomas can exceed 100 and occasionally 200. A normal result does not exclude endometriosis (sensitivity about 50 percent). |
| Benign non-gynecological causes | 35–200 U/mL, rarely higher | Cirrhosis with ascites, heart failure with effusions, pancreatitis, peritonitis, tuberculosis, lupus and recent abdominal surgery. Ascites from any cause can push CA-125 into the hundreds. |
| Postmenopausal woman with a pelvic mass | Above 35 U/mL | Meets ACOG criteria for referral to a gynecologic oncologist; about 80 percent of ovarian cancers in this setting are above this level. |
| Premenopausal woman with a pelvic mass | Above 200 U/mL | Referral threshold; lower values are common with benign disease at this age and are read with the ultrasound findings. |
| Ovarian cancer monitoring | A 50 percent fall sustained for at least 28 days defines response; doubling of the upper limit of normal on two readings defines progression | Gynecologic Cancer InterGroup (GCIG) criteria; levels usually normalize within 3 months of successful treatment. |
High CA-125
A high CA-125 means the lining cells of the abdomen, chest or reproductive tract are shedding more of this protein than usual. The degree of elevation, your age and menopausal status, and what a transvaginal ultrasound shows together decide how worrying that is. In women before menopause, a result between 35 and 100 U/mL is most often endometriosis, fibroids, adenomyosis, a functional ovarian cyst, pelvic infection, a period or early pregnancy, and ovarian cancer is uncommon at this age. Values above 200 are less often benign and prompt specialist referral when a mass is present.
After menopause the benign gynecological causes fade and the probability that a raised CA-125 reflects cancer rises, particularly when ultrasound shows a complex or solid ovarian mass. In that setting roughly four in five ovarian cancers have a CA-125 above 35 U/mL and the combination of a mass plus a high value is enough for referral to a gynecologic oncologist, whose involvement at the first operation improves outcomes. Even then, cirrhosis, heart failure, kidney disease, pancreatitis and other cancers (pancreas, lung, breast, bowel, lymphoma) remain on the list.
In a woman already diagnosed with ovarian cancer, the number is used differently. The pre-treatment value is a baseline; a fall of at least half during chemotherapy indicates response; and a confirmed rise after remission is usually the first sign of recurrence, appearing a median of 3 to 5 months before imaging or symptoms. One large randomised trial found that starting treatment on the basis of a rising CA-125 alone, before symptoms or scan changes, did not improve survival, so a rise prompts assessment rather than automatic treatment.
Common causes
Endometriosis and adenomyosis
The most common cause of a modestly raised CA-125 in women of reproductive age, usually 35 to 100 U/mL and correlating loosely with the extent of disease; endometriomas and deep infiltrating disease produce the highest values.
Menstruation, pregnancy and the first weeks after delivery
CA-125 can double during a period and rises in the first trimester as the decidua forms; both are transient and the test is best repeated after bleeding stops or later in pregnancy.
Fibroids, ovarian cysts and pelvic inflammatory disease
Degenerating fibroids, functional and hemorrhagic cysts, tubo-ovarian abscess and pelvic infection all irritate the pelvic lining and raise CA-125, often into the 50 to 150 range.
Epithelial ovarian, fallopian tube and primary peritoneal cancer
Raised in about 50 percent of stage I and 80 to 90 percent of stage III to IV disease; serous tumors produce the most, mucinous and some clear cell tumors often very little.
Other cancers
Endometrial, cervical, pancreatic, lung, breast, colorectal, gastric and liver cancers, lymphoma and mesothelioma raise CA-125 in a proportion of cases, mainly when they involve the peritoneum or pleura.
Fluid in the abdomen or chest from any cause
Ascites from cirrhosis, heart failure, nephrotic syndrome or peritoneal dialysis, and pleural effusions, stretch the mesothelium and can raise CA-125 into the hundreds without any cancer.
Peritoneal inflammation and infection
Pancreatitis, peritonitis, abdominal tuberculosis, diverticulitis, appendicitis and recent abdominal or pelvic surgery raise CA-125 for weeks.
Autoimmune and systemic disease
Lupus, rheumatoid arthritis, sarcoidosis and chronic kidney disease are associated with mild elevations.
Benign ovarian tumors and Meigs syndrome
Fibromas, thecomas and benign cystadenomas, especially when accompanied by ascites, can produce surprisingly high values that resolve after removal.
Laboratory and biological variation
Around 1 to 2 percent of healthy women run just above 35 U/mL; results from different assays are not interchangeable, so a borderline value is repeated at the same lab.
Symptoms that can go with it
- Often none, particularly with mild elevations
- Pelvic or abdominal pain, painful periods or pain with sex (endometriosis, fibroids, infection)
- Persistent bloating, abdominal swelling or clothes feeling tight around the waist
- Feeling full quickly, loss of appetite or indigestion that does not settle
- Needing to pass urine more often or urgently, or a change in bowel habit
- Unexplained weight loss or fatigue, or postmenopausal vaginal bleeding
- Breathlessness or a swollen abdomen from fluid (ascites or pleural effusion)
Normal or low CA-125
There is no lower limit of concern. A CA-125 below 35 U/mL is the expected result in most healthy women, and after menopause values of 5 to 15 U/mL are typical. In a woman being followed after ovarian cancer treatment, a CA-125 that has fallen into the normal range and stays there is one of the main signs that the cancer is in remission, although it is always read alongside examination and scans.
A normal CA-125 does not rule ovarian cancer out. About half of stage I cancers, and most mucinous and some clear cell and borderline tumors, produce little or none. It also does not exclude endometriosis, where the test is positive in only about half of confirmed cases. Persistent bloating, pelvic pain, early fullness or urinary frequency in a woman over 50 should be assessed with ultrasound regardless of a normal CA-125.
Common causes
Good health
The usual reason. Levels are lowest after menopause and in women who have had a hysterectomy.
A cancer that does not shed CA-125
Mucinous, clear cell, low-grade and early-stage ovarian cancers, and borderline tumors, are frequently CA-125 negative.
Successful treatment
After complete surgical removal and chemotherapy, CA-125 falls with a half-life of about 6 days and is usually normal within 3 months.
Endometriosis that does not raise it
Superficial peritoneal endometriosis in particular often leaves CA-125 normal; the diagnosis rests on symptoms, examination, imaging and sometimes laparoscopy.
Assay differences
A result that is borderline on one manufacturer's assay can read normal on another; monitoring should use one laboratory.
Symptoms that can go with it
- None; a normal CA-125 does not cause symptoms
- Persistent pelvic or abdominal symptoms still need an ultrasound, because CA-125 misses half of early ovarian cancers
Read it alongside
- Transvaginal ultrasound — not a blood test, but the single most important companion; CA-125 is rarely interpreted without it when a mass is the question.
- HE4 — combined with CA-125 in the ROMA score to sort a pelvic mass into low or high risk; HE4 is less affected by endometriosis and menstruation.
- CEA and CA 19-9 — raised CEA with a modest CA-125 points to a bowel, pancreatic or mucinous tumor rather than typical ovarian cancer.
- hCG, AFP and LDH — germ cell tumor markers, checked instead of or alongside CA-125 in women under 40 with an ovarian mass.
- FSH and estradiol — confirm menopausal status, which changes the referral threshold from 200 to 35 U/mL.
- ALT, albumin and a liver panel — cirrhosis and ascites are common non-cancer causes of a high CA-125.
- BNP — heart failure with effusions raises CA-125, and the two markers rise together.
- CRP and white cell count — pelvic infection, pancreatitis and peritonitis raise both CA-125 and inflammatory markers.
What usually happens next
- A raised CA-125 is almost always paired with a transvaginal ultrasound; if that is normal and you are premenopausal, the test is usually repeated after your next period, or in 4 to 6 weeks, before anything further is done.
- If ultrasound shows a mass, your clinician will combine the CA-125 with the ultrasound features and your menopausal status (Risk of Malignancy Index or ROMA with HE4); a postmenopausal value above 35 U/mL, or a premenopausal value above 200, meets the threshold for referral to a gynecologic oncologist.
- Ask whether a benign driver explains the result: endometriosis, fibroids, a recent period, pregnancy, pelvic infection, liver or heart disease, or recent surgery.
- If you are being followed after ovarian cancer treatment, ask what your baseline is and what change would prompt a scan; CA-125 is usually checked every 2 to 4 months for 2 years, then less often.
- A persistently raised CA-125 with a normal pelvis is investigated for non-gynecological causes with a chest X-ray or CT, liver tests and sometimes an abdominal CT.
Diet, lifestyle and natural levers with evidence
What can move CA-125 once the cause is known. Nothing here replaces finding the cause.
Time the test correctly
Strong evidenceNothing dietary or herbal lowers CA-125, but when you test changes the number. Levels can double during menstruation, are raised through the first trimester of pregnancy and for a few weeks after delivery, and stay up for several weeks after abdominal or pelvic surgery, pelvic infection or pancreatitis. Testing in the first half of the cycle once bleeding has stopped, and waiting 4 to 6 weeks after an acute illness or operation, avoids most false alarms.
Treat the benign driver, then recheck
Moderate evidenceWhen endometriosis is the cause, hormonal suppression prescribed by a clinician lowers CA-125 over 3 to 6 months in step with symptom control, and surgical removal of endometriomas drops it further. Draining ascites or effusions, treating heart failure, and recovery from pelvic infection all bring CA-125 down with a half-life of about 6 days. A level that falls as the benign condition improves is reassuring; one that keeps rising needs another explanation.
Do not assume a value above 200 U/mL, or one that is rising on repeat testing, is explained by a benign condition until a mass has been excluded on ultrasound.
What lowers ovarian cancer risk (the thing CA-125 is used for)
Moderate evidenceNo supplement or diet changes CA-125 or has been shown to prevent ovarian cancer. In pooled case-control data from over 9,900 women with ovarian cancer, any breastfeeding was associated with about 24 percent lower risk, and longer total duration with greater reduction; higher parity and years of combined oral contraceptive use are the other well-established protective factors, while obesity is a modest risk factor. These are population associations, not individual guarantees, and do not change how a raised result is handled.
When to see a clinician promptly
- A CA-125 above 35 U/mL after menopause, or above 200 U/mL at any age, especially with an ovarian mass on ultrasound: ask for referral to a gynecologic oncologist rather than a general surgeon.
- A rising CA-125 on repeat testing, even if you feel well, or a rise after ovarian cancer treatment.
- Persistent bloating, abdominal swelling, pelvic pain, feeling full quickly or urinary urgency lasting more than 2 to 3 weeks, whatever the CA-125 result.
- Sudden severe pelvic pain with nausea or fainting, which can mean a twisted or ruptured ovarian cyst and is an emergency.
- Fever with pelvic pain and discharge, which can mean pelvic inflammatory disease and needs same-day treatment.
- A swollen abdomen with breathlessness, which can mean ascites or a pleural effusion needing prompt assessment regardless of cause.
Frequently asked questions
What is a normal CA-125 level?
Under 35 U/mL is normal on most assays, though some labs use 30 or 38. Healthy postmenopausal women typically run between 5 and 15 U/mL, and premenopausal women somewhat higher, with transient rises during periods and early pregnancy. U/mL and kU/L are the same number. About 1 to 2 percent of healthy women sit just above the cut-off without any disease.
Is a CA-125 of 40, 60 or 100 high?
All three are above the usual 35 U/mL cut-off, but what they mean depends on age and ultrasound. Before menopause, values of 40 to 100 are most commonly endometriosis, fibroids, a cyst, a period, pregnancy or pelvic infection, and cancer is uncommon. After menopause, any value above 35 with an ovarian mass is a referral trigger. In either case the result is repeated and read with a transvaginal ultrasound rather than acted on alone.
What CA-125 level indicates ovarian cancer?
There is no level that diagnoses it; only surgery and pathology can. The higher the value and the older the woman, the greater the probability: in a postmenopausal woman with a complex ovarian mass, a CA-125 above 35 U/mL makes cancer likely enough for specialist referral, and values above 200 in any woman with a mass are high-risk. Equally, half of early ovarian cancers have a normal CA-125, so a normal result does not exclude it.
Can endometriosis cause high CA-125?
Yes, and it is the most common cause of a raised result in women of reproductive age. Values are usually 35 to 100 U/mL, higher with endometriomas and deep disease, and fall with hormonal treatment. The test is too insensitive to diagnose endometriosis (it is normal in about half of confirmed cases) and too non-specific to prove it, so the diagnosis rests on symptoms, examination, ultrasound or MRI, and sometimes laparoscopy.
Why is CA-125 not used to screen for ovarian cancer?
Because it misses half of early cancers and is raised by many benign conditions, so screening healthy women produces false reassurance and unnecessary operations. The US PLCO trial (78,000 women) and the UK UKCTOCS trial (over 200,000 women) both found that annual CA-125 testing, even with ultrasound, did not reduce ovarian cancer deaths. The US Preventive Services Task Force recommends against screening women at average risk. Women with BRCA mutations or Lynch syndrome are managed differently and should discuss surveillance with a specialist.
Can CA-125 be high without cancer?
Very often. Menstruation, pregnancy, endometriosis, fibroids, adenomyosis, ovarian cysts, pelvic inflammatory disease, cirrhosis with ascites, heart failure, pancreatitis, peritonitis, tuberculosis, lupus, kidney disease and recent abdominal surgery all raise it. In premenopausal women the large majority of raised results have a benign cause. Values above 200 U/mL are less often benign but still occur with ascites, endometriomas and pelvic infection.
How is CA-125 used after ovarian cancer treatment?
It is measured every 2 to 4 months for the first 2 years and then less often. A level that has returned to normal and stays there is reassuring. A confirmed rise, usually defined as a doubling of the upper limit of normal on two readings, typically precedes a scan abnormality by 3 to 5 months and prompts imaging. A large trial found no survival benefit from restarting chemotherapy on the CA-125 rise alone before symptoms or scan changes, so the decision is individual.
Does CA-125 rise during a period or pregnancy?
Yes. It can roughly double during menstruation and is raised through the first trimester, often to 35 to 65 U/mL and occasionally higher, before settling. If your sample was taken during a period, or you are in early pregnancy, a mildly raised result is usually repeated at a better time rather than investigated further.
References
- CA-125 blood test (ovarian cancer). MedlinePlus, US National Library of Medicine (2023)View source
- CA 125 test. Mayo Clinic (2023)View source
- American College of Obstetricians and Gynecologists. Practice Bulletin No. 174: Evaluation and management of adnexal masses. Obstetrics & Gynecology (2016)
- Menon U, Gentry-Maharaj A, Burnell M, et al.. Ovarian cancer population screening and mortality after long-term follow-up in the UK Collaborative Trial of Ovarian Cancer Screening (UKCTOCS): a randomised controlled trial. The Lancet (2021)
- Buys SS, Partridge E, Black A, et al.. Effect of screening on ovarian cancer mortality: the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening randomized controlled trial. JAMA (2011)
- US Preventive Services Task Force. Screening for ovarian cancer: US Preventive Services Task Force recommendation statement. JAMA (2018)
- Hirsch M, Duffy J, Davis CJ, et al.. Diagnostic accuracy of cancer antigen 125 for endometriosis: a systematic review and meta-analysis. BJOG (2016)
- Rustin GJ, van der Burg ME, Griffin CL, et al.. Early versus delayed treatment of relapsed ovarian cancer (MRC OV05/EORTC 55955): a randomised trial. The Lancet (2010)
- Moore RG, McMeekin DS, Brown AK, et al.. A novel multiple marker bioassay utilizing HE4 and CA125 for the prediction of ovarian cancer in patients with a pelvic mass. Gynecologic Oncology (2009)
- Rustin GJ, Vergote I, Eisenhauer E, et al.. Definitions for response and progression in ovarian cancer clinical trials incorporating RECIST 1.1 and CA 125 agreed by the Gynecological Cancer Intergroup (GCIG). International Journal of Gynecological Cancer (2011)
- Babic A, Sasamoto N, Rosner BA, et al.. Association between breastfeeding and ovarian cancer risk. JAMA Oncology (2020)
- Jacobs I, Bast RC Jr. The CA 125 tumour-associated antigen: a review of the literature. Human Reproduction (1989)
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