Cancer Antigen 125 (CA 125) Test

CA-125 stands for cancer antigen 125. It is a glycoprotein that is normally present in small amounts in the body. However, its levels may increase in certain health problems (mainly cancer).

The CA-125 test is a blood test that measures the level of CA-125 in the blood. This protein is also known as a tumour marker because its levels can increase in certain types of cancer, especially ovarian cancer (where cells in the ovary grow abnormally).

Doctors use the CA-125 test mainly to help evaluate suspected ovarian cancer and to monitor patients who have already been diagnosed. This test also helps check how well the treatment is working and the recurrence of cancer.

You may need a CA-125 test in the following situations:

• If you have a pelvic lump, growth on imaging tests like ultrasound, or symptoms that may indicate cancer: This test may help in evaluation if your doctor finds a lump in your pelvis or suspects ovarian cancer due to a growth on imaging tests or symptoms like unexplained loss of appetite or weight, bloating, nausea, vomiting, diarrhoea, constipation, pelvic pain, vaginal or rectal bleeding. However, only a biopsy (checking tissue or cells for abnormal growth) can confirm cancer.
• If you are at high risk of ovarian cancer: Your doctor may recommend this test if you have a higher risk of developing ovarian cancer due to factors such as:
• A personal history of breast, uterine, or colorectal cancer
• A close family history of ovarian cancer (mother, sister, or multiple relatives with ovarian cancer)
• Family history of breast or colorectal (colon) cancer
• Genetic conditions like mutations in the gene (BRCA1 or BRCA2) or Lynch syndrome (a disorder that increases the risk of certain cancers)
• If you have ovarian cancer: To follow up on how well your treatment is working or to see if the cancer has come back after treatment.

The frequency of the CA-125 test may vary depending on your condition and your doctor’s advice.2–5

Note: CA-125 testing frequency and interpretation must always be done under a doctor’s supervision, as levels can be influenced by various non-cancerous causes.

The CA-125 test helps doctors understand what may be happening in your body, especially in relation to ovarian cancer. However, it is not a definitive diagnostic test and is always interpreted along with other tests and clinical findings. Here’s what this test may help with:

• Supporting diagnosis when cancer is suspected: High CA-125 levels in someone with a pelvic lump may suggest ovarian cancer. Doctors will need additional tests (like imaging or biopsy) to confirm the diagnosis of cancer.
• Monitoring ovarian cancer treatment: If CA-125 levels decrease over time, it usually means the treatment is working. And if levels stay the same or increase, it may suggest the treatment is not effective.
• Detecting cancer recurrence: If CA-125 levels increase after treatment is completed, it may suggest cancer recurrence.
• Benign (non-cancerous causes): These include conditions, such as endometriosis, pelvic inflammatory disease, liver disease, pregnancy, and benign ovarian cysts.

What to Expect Before the CA-125Test

No fasting is required for a standalone CA-125 test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raiseCA-125 levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the CA-125 Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

The CA-125 test measures a single parameter:

• The level of cancer antigen 125 (CA-125) protein in the blood.

This protein is made by epithelial cells in the female reproductive organs, such as the ovaries and fallopian tubes. CA-125 levels can increase when these organs are inflamed, for example, during a menstrual period. However, higher levels are also seen in individuals with ovarian cancer. Therefore, CA-125 is also known as an ovarian cancer marker.

The CA-125 normal range is given in the table below.

Note:

• The normal range may vary slightly depending on the laboratory and testing method used.
• A single CA-125 result is not enough to diagnose or rule out ovarian cancer. Serial trends (changes in CA-125 over time) are more meaningful to doctors.
• Results should always be interpreted along with symptoms, medical history, and other tests if needed.

Note:

• CA-125 levels can be high in non-cancerous conditions such as menstruation. So, a high CA-125 level does not always mean cancer.
• Always consult your doctor for proper evaluation and further testing if required.

The CA-125 blood test involves a simple blood sample, so risks are minimal. You may feel slight pain, bruising, or bleeding at the needle site, but it usually goes away quickly. Like all medical tests, this test also has certain limitations, which may include the following:

• CA-125 is not specific to ovarian cancer. It may also increase in normal conditions like early pregnancy and menstruation, and in non-cancerous diseases such as pelvic inflammatory disease (PID), endometriosis, hepatitis, and liver cirrhosis.
• High doses of biotin (vitamin B7 >5 mg/day) might affect the test results. Therefore, it is recommended to wait at least 8 hours after the last dose before giving a sample.
• In rare instances, very high levels of antibodies (such as human anti-mouse antibodies [HAMA]) against the substances used during laboratory testing may interfere with the test and affect its accuracy.
• This test is mainly used for monitoring ovarian cancer rather than screening in the general population.

If your CA-125 levels are abnormal or if there is suspicion of ovarian cancer, your doctor may recommend additional tests for confirmation and evaluation:

• Complete blood count (CBC)
• Pelvic ultrasound
• Biopsy
• Other tumour markers (tests such as human epididymis protein 4 [HE4] or risk of ovarian malignancy algorithm [ROMA]

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