Ovarian Cancer Blood Test Information

Many people come in startled after being told at a health checkup that "an ovarian cyst is seen," or after seeing the CA-125 figure written on the result slip. One of the questions I most often receive in the clinic is, "Can I know ovarian cancer in advance with a blood test?" To put the conclusion first, a blood test is not a standalone tool for diagnosing or screening ovarian cancer. It is, however, a supplementary marker that gains meaning when a doctor interprets it together with other information. In this article, I will lay out, along with authoritative recommendations, how far ovarian cancer markers including CA-125 can tell you and from where they cannot.

The reason ovarian cancer is tricky lies in its location and symptoms. The ovaries are deep in the pelvic abdominal cavity, so they are not palpable from the outside, and in the early stage the symptoms are vague. They often appear as gastrointestinal symptoms such as bloating, abdominal distension, and indigestion, so they are mistaken for a digestive problem and diagnosis is sometimes delayed.

In fact, a substantial number of patients are found when the cancer has progressed to some degree. When diagnosed at an advanced stage, the prognosis becomes difficult, whereas the earlier it is found, the better the course is reported to be. The age of onset is most common around the fifties, followed by the sixties and then the forties. It is precisely for this reason that the expectation "couldn't I just draw blood once and know in advance" arises, and it is also why we must understand marker tests accurately.

CA-125 is the blood marker classically most widely used in ovarian cancer care. First developed in 1981 by an immunoassay using a monoclonal antibody, it has been used to gauge the detection and degree of progression of ovarian cancer in serum. Today the CA-125 item is included in most health checkup packages, so many people encounter this figure on their result slip.

But here lies the biggest misunderstanding. CA-125 is not "a number that goes up if you have ovarian cancer," but "a number that can go up in various situations." To read the test result accurately, you first have to know what this figure responds to. The moment you take just one figure in isolation and judge it as high or low, the test instead becomes a tool that calls forth unnecessary anxiety and testing.

The reasons CA-125 is hard to use as a screening tool are the following limitations. These are items I often point out when explaining to patients in the clinic.

• In a substantial number of early ovarian cancers, CA-125 does not rise, so a normal figure does not necessarily mean reassurance.
• The figure also rises in benign gynecologic conditions such as benign ovarian tumors, pelvic inflammatory disease, and endometriosis.
• It can also fluctuate in normal physiological states such as pregnancy or menstruation.
• It can also be elevated in some other medical conditions.

In summary, CA-125 has low specificity and sensitivity that stays around half, so by itself it is hard to be a reliable criterion for early diagnosis. If symptoms such as abnormal bleeding or pelvic pain accompany it, checking the cause of symptoms such as abnormal vaginal bleeding comes before the figure.

What is used together to supplement these limitations is HE4 (Human Epididymis Protein 4). HE4 is a glycoprotein made by the WFDC2 gene; it is also distributed in normal tissue but has the characteristic of being overexpressed in pathological tissue, so it is reported to show good performance in ovarian cancer detection. The important point is that HE4 is expressed independently of CA-125. Because they look at different signals, combining the two helps raise diagnostic sensitivity at stages 1 and 2.

Going one step further from here is ROMA (Risk of Ovarian Malignancy Algorithm). It is a risk index calculated by putting together the HE4 and CA-125 figures and menopausal status, and is used to "screen" whether a pelvic tumor that has been found is closer to malignant or to benign.

As the table shows, the proper place of these tests is "risk assessment and follow-up for those in whom a tumor or symptom has already been confirmed," not a screening test that filters out people with no symptoms at all. If you are curious about interpretation of test results, feel free to inquire through a gynecologic symptom check consultation.

This is the most important part. For ordinary women who have no symptoms and no high-risk factors such as family history, ovarian cancer screening using CA-125 or ultrasound is not recommended.

The U.S. Preventive Services Task Force (USPSTF, 2018 recommendation) recommended not performing ovarian cancer screening in asymptomatic average-risk women. The reason was that there is insufficient evidence that any of CA-125, transvaginal ultrasound, or a combination of the two lowers ovarian cancer mortality, while harm can outweigh benefit, such as false positives leading to unnecessary surgery even when there is no cancer. The American College of Obstetricians and Gynecologists (ACOG) likewise does not recommend CA-125 or transvaginal ultrasound for screening purposes in women without strong risk factors, and takes the position that there is no ovarian cancer screening test recommended for average-risk women.

So the expectation that "a blood test tells you ovarian cancer" differs from fact. A normal figure does not guarantee reassurance, and a high figure does not by itself mean cancer. Even if CA-125 is included on your checkup result slip, it is more accurate to receive that number not as a diagnosis but as "a starting point to be interpreted together with a specialist."

That screening is not recommended by no means implies you should sit idle. Only the direction needs to change. What is clinically more important is not a single figure but sensitivity to symptoms and management tailored to risk.

• If you have abdominal distension, pelvic or lower-abdominal pain, a quickly-full feeling, or frequent urination that persists for more than 2 weeks or gradually worsens, it is good to get care.
• High-risk groups with genetic mutations such as BRCA1 and BRCA2 or a family history may need an individualized follow-up strategy, unlike the general recommendation. In this case, a consultation about information that genetic testing can reveal and premium genetic testing helps.
• A realistic early-detection strategy is to look after not only the ovaries but other conditions such as the uterus and cervix together, through regular gynecologic checkups and life-stage screening. The value of screening has also been covered in why regular checkups matter and the story of uterine fibroid examination.

In my clinical experience, those who notice "a body signal different from usual" more than the number on the result slip often reach a faster, more accurate diagnosis.

CA-125, HE4, and ROMA are certainly useful tools, but their use lies not in "standalone diagnosis" but in being "one piece of comprehensive judgment." Even the same figure is interpreted completely differently depending on age, menopausal status, symptoms, ultrasound findings, and risk factors. So what is more important than the test is how you read that result and decide on the next step.

If the CA-125 figure on your checkup result slip is on your mind, or if you have found an ovarian cyst and feel lost about what to do, I recommend consulting a specialist rather than searching alone and growing anxious. Accurate information is the most solid reassurance.

Written by: Lee Dong-hee Director · OB-GYN specialist · View doctor profile

First published June 5, 2024 · Last reviewed May 30, 2026

References: U.S. Preventive Services Task Force, Ovarian Cancer Screening (2018), American College of Obstetricians and Gynecologists (ACOG), Ovarian Cancer patient guidance materials

This article is intended to provide general health information and does not replace individual diagnosis or treatment. If you have symptoms, please consult through a medical visit.