CA-125 is a substance made by most ovarian cancers, which is why it is called the "ovarian tumour marker". But healthy tissues make it too, and most of the time a high level does not mean cancer [2, 9]. The usual upper limit is 35 units per millilitre [3]; periods, pregnancy, endometriosis, fibroids, liver disease, heart failure and fluid in the abdomen or around the lungs can all raise it [1, 2, 9]. A high CA-125 means more after the menopause; the doctor reads it together with your symptoms and a pelvic ultrasound scan [4, 7].
Key points
- Most people with a high CA-125 do not have ovarian cancer; many harmless conditions raise this number [1, 9].
- Before the menopause, harmless causes such as periods and endometriosis are more common. After the menopause, a high CA-125 needs to be taken more seriously, and an ultrasound scan of the abdomen and pelvis is usually needed [2, 4].
- A normal CA-125 does not completely rule out cancer either: in the earliest stage of ovarian cancer (stage 1), half of patients or fewer have a raised CA-125 [3].
- CA-125 is not recommended as a check-up test for women without symptoms: in a large study of more than 200,000 women after the menopause, a yearly test did not reduce the number of deaths from ovarian cancer [10].
What is CA-125 in a blood test?
CA-125 is a protein that most ovarian cancer cells make and release into the blood [2]. But healthy people make it too; for example, in the lining of the womb and the cervix, and in the thin membranes that cover the lungs, the heart and the inside of the abdomen [2]. So anything that irritates or inflames these membranes can raise CA-125 [2].
CA-125 is also called the "ovarian tumour marker". It has two main jobs: helping to assess suspicious growths on the ovary, especially after the menopause, and following the treatment of people who have ovarian cancer [2, 12]. Read about tumour markers in general: What is a tumour marker?; and about two other common tumour markers: CA 19-9 and AFP.
What should CA-125 be? (normal range)
In most laboratories, the upper limit of normal for CA-125 is about 35 units per millilitre, and this limit is the same for women before and after the menopause [3]. Compare your number with the range printed on your lab report.
- CA-125 is naturally higher in women before the menopause and falls with age [2].
- About 1 in 20 healthy women have a CA-125 above 35; but a level above 100 is very rare in healthy women, about 1 in 1,000 [2].
- A number below 35 is not always fully reassuring either. For women aged 50 and over with worrying symptoms, the national guideline in England has set the limit a little below 35, so that an ultrasound scan is arranged even at lower levels [4].
What besides cancer can raise CA-125?
| Cause | Explanation |
|---|---|
| Periods | Higher in the days before and during a period [2, 3] |
| Pregnancy and childbirth | May rise in the first three months of pregnancy, and from delivery until two days afterwards [1, 2] |
| Endometriosis and endometriosis cysts of the ovary | An important cause of high results before the menopause; the more severe the endometriosis, the more likely CA-125 is to be raised [3, 8] |
| Fibroids and harmless ovarian cysts | In one hospital review, these were common causes of high results without ovarian cancer [9] |
| Inflammation or infection in the pelvis and abdomen | Irritation or inflammation of the inner lining of the pelvis and abdomen raises CA-125 [2, 3] |
| Liver disease, especially cirrhosis | CA-125 is raised in most people with cirrhosis [1, 2] |
| Heart failure | CA-125 also rises in heart failure [1, 2] |
| Fluid in the abdomen (ascites) or around the lungs | Whatever its cause [1] |
| Other cancers | Such as cancer of the womb (endometrium), breast, lung, pancreas, bowel and stomach [2, 9] |
A single high number is never enough to diagnose any illness; the doctor reads it together with your symptoms, an examination and an ultrasound scan.
How does a high CA-125 differ before and after the menopause?
Before the menopause: harmless causes such as periods and endometriosis are common, and at this age CA-125 more often gives a "high result for no reason" [2]. The national guideline in England says that in women under 40 the decision should not be based on CA-125 alone; if symptoms continue, it suggests an ultrasound scan of the abdomen and pelvis [4]. In women under 40 who may have ovarian cancer, two other blood tests, AFP and beta-hCG, are also measured so that less common types of ovarian tumour are not missed [5]. Read more: What does a high AFP mean?
After the menopause: harmless causes are less common and a high CA-125 means more [2]. In a UK study of 22,000 women after the menopause who had no symptoms, of every 100 women with a CA-125 of 30 or more, about 3 developed cancer of the ovary or fallopian tube in the following years [7]. The higher the number, the higher this chance; with a number above 100, about 1 in 7 [7]. So even with a high number, most of these women did not develop cancer, but an ultrasound check is needed [4, 7].
I have an ovarian cyst; do I need a tumour marker test?
If an ultrasound scan shows a cyst or growth on the ovary and the doctor suspects cancer, they usually ask for CA-125 as well [5, 12]. They combine the CA-125 result with how the cyst looks on ultrasound and whether you have been through the menopause, in a simple score called the "risk of malignancy index" [5, 6]. This combination is more accurate than any of the three on its own [6]. If the score is high, the national guideline in England recommends referral to a specialist gynaecological cancer team [5].
Endometriosis cysts of the ovary also raise CA-125; so a high result with these cysts does not mean cancer [3]. Read about the difference between harmless and cancerous growths: What is the difference between a benign and a malignant tumour?
Is the CA-125 test useful as a check-up or screening test?
For women who have no symptoms and no high inherited risk, a CA-125 test is not recommended as a check-up [1, 10]. In the largest study, more than 200,000 women after the menopause in the UK were followed for about 16 years. A yearly CA-125 test with an ultrasound scan found the disease earlier in some women, but the number of deaths from ovarian cancer did not fall [10]. In a large study in the USA, a yearly CA-125 test and ultrasound scan did not reduce deaths from ovarian cancer either [1]. High results with no cause found can also lead to unnecessary operations and worry [2].
These studies were about women at average risk [1, 10]. If several of your close relatives have had ovarian or breast cancer, or an inherited mutation such as BRCA runs in your family, talk to your doctor about genetic counselling: Is cancer hereditary? and Which screening tests do I need?
CA-125 after the diagnosis and treatment of ovarian cancer
In people who have ovarian cancer, CA-125 helps show whether treatment is working; a fall during chemotherapy is a good sign [2]. After treatment ends, it is usually measured for follow-up together with an examination and, when needed, a CT scan [12].
A new rise in CA-125 can show that the disease has come back months before any symptoms [11]. But in a large study, starting chemotherapy earlier only because CA-125 had risen, before any symptoms appeared, did not help patients live longer [11]. So how often CA-125 is measured, and what to do if it rises, is a decision you make with your care team [2, 11]. Read more: What is cancer recurrence and how is it followed up?
What does a high CA-125 mean in men?
Men do not have ovaries, but their bodies make CA-125 too, and it can be raised [2, 9]. The causes are the same non-gynaecological causes seen in women: liver disease and cirrhosis, heart failure, fluid in the abdomen or around the lungs, and some cancers such as cancer of the lung, pancreas, bowel and stomach [1, 2]. In a hospital review in the UK, almost half of the men who had this test had a high result [9].
A single high number does not make a diagnosis. The doctor finds the cause by asking about symptoms, examining you, checking liver blood tests and, if needed, arranging a scan.
When should I call my doctor?
Always show your CA-125 result to the doctor who ordered it; a single number is neither a reason to worry nor a reason to feel reassured. In these situations do not wait, and see a doctor soon:
- bloating or a swollen abdomen, feeling full quickly or loss of appetite, pelvic or abdominal pain, or needing to pass urine more often or more urgently that is persistent or keeps coming back (particularly more than 12 times a month), especially after the age of 50 [4]
- unexplained weight loss, new tiredness or a change in bowel habit [4]
- a lump in the abdomen or pelvis, or an abdomen that looks swollen and full of fluid [4]
- if you have had ovarian cancer and your CA-125 has risen during follow-up, contact your care team [12]
Sudden severe abdominal or pelvic pain, repeated vomiting or shortness of breath needs urgent care: call your local emergency number.
Frequently asked questions
My CA-125 is a little above 35; should I worry?
A number a little above 35 is common and most of the time has a harmless cause, especially before the menopause [2, 9]. The doctor considers your age, whether you have been through the menopause, the timing of your period and your symptoms; they may ask for a pelvic ultrasound scan [4, 5]. The higher the number, especially after the menopause, the more important it is to check [7].
Does an elevated CA-125 mean ovarian cancer?
No. In one hospital review, of every 5 women with a high CA-125 who were tested because cancer was suspected, only 1 had ovarian cancer. The others had other conditions, including other cancers, harmless ovarian cysts and fibroids [9]. To find out, the doctor usually asks for an ultrasound scan of the abdomen and pelvis [4, 12].
Does CA-125 rise in endometriosis?
Yes, often. In a review of studies, about half of women with endometriosis had a CA-125 of 30 or more; this was more common in moderate and severe endometriosis than in mild endometriosis [8]. But a normal CA-125 does not rule out endometriosis [8]. Endometriosis cysts of the ovary also raise CA-125 [3].
My CA-125 is normal; does that mean I do not have ovarian cancer?
Not necessarily. About 1 in 5 ovarian cancers make no CA-125 at all [2], and in the earliest stage of the disease (stage 1), half of patients or fewer have a raised CA-125 [3]. If you have symptoms such as persistent bloating, feeling full quickly or pelvic pain that become more frequent or persistent, see your doctor again despite a normal result [4]. Read about the symptoms: What are the symptoms of ovarian cancer?
Does CA-125 rise in pregnancy?
Does CA-125 also rise in womb (endometrial) cancer?
Sometimes; CA-125 also rises in some other cancers, including womb cancer [2]. Always have bleeding after the menopause checked promptly; the national guideline in England recommends urgent referral for it [4]. Read more: What are the symptoms of womb (endometrial) cancer?
Thresholds, the RMI and key evidence (for doctors)
For physicians
| Age group (years) | CA-125 threshold |
|---|---|
| 40 to 49 | 35 IU/mL or greater |
| 50 to 59 | 31 IU/mL or greater |
| 60 to 69 | 24 IU/mL or greater |
| 70 to 79 | 25 IU/mL or greater |
| 80 and over | 31 IU/mL or greater |
Aged 39 and under: do not use CA-125 in isolation for decision making; consider an urgent direct-access ultrasound scan (recommendation 1.5.6).
NICE NG12 (2026). In women with persistent or frequent symptoms, particularly more than 12 times per month (abdominal distension, early satiety and/or loss of appetite, pelvic or abdominal pain, urinary urgency and/or frequency), measure CA-125 in primary care in those aged 40 and over and arrange an urgent ultrasound scan according to the age-based thresholds in the table above (recommendations 1.5.8 and 1.5.9); ascites and/or a pelvic or abdominal mass on examination (not obviously uterine fibroids) warrants a suspected cancer pathway referral (1.5.1). The committee emphasised not labelling a CA-125 below 35 as "normal"; in those aged 39 and under, because of the low prevalence and the risk of false reassurance, CA-125 alone should not guide decisions [4].
NICE CG122. In women under 40 with suspected ovarian cancer, also measure AFP and beta-hCG to identify women who may not have epithelial ovarian cancer. RMI I = U × M × CA-125; the ultrasound score gives 1 point for each of multilocular cyst, solid areas, metastases, ascites and bilateral lesions (U=0 for a score of 0, U=1 for a score of 1, U=3 for a score of 2 to 5); M=1 premenopausal and M=3 postmenopausal (no period for more than 1 year, or over 50 with a previous hysterectomy). RMI I of 250 or more: refer to a specialist multidisciplinary team [5]. In the original Jacobs study (101 benign and 42 malignant masses), a CA-125 of 30 U/mL had a sensitivity of 81% and a specificity of 75%, and the RMI at a cut-off of 200 had a sensitivity of 85% and a specificity of 97% [6]. For premenopausal women with a pelvic mass, ACOG has proposed, based on expert opinion, a cut-off of 200 U/mL for referral to a gynaecological oncologist [2].
Test performance. The upper limit of 35 U/mL has not changed since the original assay (1983); about 5% of healthy women are above 35 and about 0.1% above 100 U/mL, and about 20% of ovarian cancers do not express CA-125 [2]. Elevation has been reported in only 23% to 50% of stage I cases [3]. In asymptomatic postmenopausal women (22,000 women, mean follow-up 6.76 years), the cumulative risk of invasive epithelial ovarian or fallopian tube cancer was 0.030 with a CA-125 of 30 U/mL or more and 0.149 with more than 100 U/mL, compared with 0.0022 in the whole study population [7]. In an audit of 799 patients, only 20% of abnormal results in women tested for suspected malignancy were due to ovarian cancer; false positives were mainly another malignancy (26%), benign ovarian disease (14%) and benign gynaecological conditions, particularly leiomyomas (9%); 22 of 48 men (46%) had an abnormal result, and specificity for ovarian cancer increased at concentrations above 1000 kU/L [9]. In endometriosis (14 studies, 2920 participants, cut-off 30 U/mL), pooled specificity was 93% and sensitivity 52%; sensitivity was 63% in moderate to severe disease versus 24% in minimal disease [8].
Screening and follow-up. UKCTOCS (202,562 postmenopausal women aged 50 to 74, median follow-up 16.3 years): multimodal screening with CA-125 (ROCA algorithm) increased stage I incidence by 47.2% and reduced stage IV by 24.5%, but did not significantly reduce deaths from ovarian and tubal cancer (0.6% in all three groups; P=0.58 for multimodal screening) [10]. In PLCO (annual CA-125 at a 35 U/mL threshold for 6 years and TVU for 4 years), ovarian cancer mortality was not reduced after a median follow-up of 17 years (rate ratio 1.18; 95% CI 0.98 to 1.4) [1]. In MRC OV05/EORTC 55955 (529 patients in complete remission after platinum-based chemotherapy), early treatment based on a CA-125 rise above twice the upper limit of normal, compared with treatment at clinical relapse, did not improve survival (HR 0.98; 95% CI 0.80 to 1.20; median survival 25.7 months with early treatment vs 27.1 months with delayed treatment) [11]. ESMO (Pan-Asian adaptation 2025): diagnostic work-up should include CA-125, pelvic ultrasound by an expert examiner and CT of the thorax, abdomen and pelvis [III, A]; surveillance can include CA-125, physical examination and CT [IV, B] [12].
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References
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