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CA 15-3 Tumor Marker Test for Women: Why and How is it Done?

Medically reviewed by John Paul Abrina, MD · Oncology · Davao Doctors Hospital

Written by Nikita Bhalla · Updated Jul 13, 2022

    CA 15-3 Tumor Marker Test for Women: Why and How is it Done?

    The CA 15-3 tumor marker blood test evaluates the levels of CA 15-3 or cancer antigen 15-3 in the human blood. Antigen refers to a substance that stimulates the defense system of the body. The CA 15-3 antigen is released into the human blood by certain types of cancer cells.

    This test is used to monitor certain types of cancer. Although most commonly used to monitor breast cancer, high levels of this antigen may also indicate other malignancies as well as benign (non-malignant) conditions.

    Such antigens are also called tumor markers as they are known for offering information about the developing cancer.

    Why is a CA 15-3 tumor marker blood test done?

    A blood test is not recommended for diagnosing the presence of breast cancer. It is advised for monitoring the extent of development and severity of certain cancers like breast cancer.

    But the CA 15-3 blood test is not restricted to monitoring breast cancer only. It can track the growth of other malignant disorders and also non-malignant conditions. However, the test results may not be conclusive about the presence of breast cancer. Advanced breast cancer may have tumors that do not make CA 15-3.


    There are a few things that patients need to do before having the test done. Certain blood tests may require patients to keep a complete or partial fast for a certain number of hours before undergoing the tests. A partial fast requires avoiding food, while a complete fast implies abstaining from food and water.

    The duration of fast may vary between 6 to 12 hours approximately. However, these regulations are not applicable for the CA 15-3 tumor marker blood test, unless your doctor recommends otherwise. 

    It is essential for you to discuss with your doctor the medications that you may be taking now or have taken in the recent past. Such medications include prescription drugs, non-prescription or OTC (over-the-counter) drugs, vitamins, supplements, and herbals.

    Make sure to carry your medical documents for the doctor to thoroughly check the prescription drugs that you might be taking now. This will enable him/her to analyze whether any of these medications have a known history of interacting with this blood test result. He/she will then be able to advise you accordingly. 

    tumor marker test

    Understanding the Results

    Your test results depend on several factors like your age, gender, medical history, test method, and other aspects. It is necessary to talk to your doctor about your test results, rather than self-diagnosing your condition. Your doctor is the best person to make you understand what your result means.

    Negative or normal result: Cancer antigen 15-3 of less than or equal to 30 units per milliliter (U/mL) is considered to be the normal range. This is referred to as a negative result, indicating the absence of malignant or non-malignant growth.

    Positive: It is important to know that having a positive CA 15-3 blood test does not necessarily imply the presence of breast cancer or recurrence of the condition. Other malignant tumor or non-malignant conditions may also have led to a positive result.

    Non-malignant conditions like benign tumors of the ovary, breast, and liver may also cause a rise in CA 15-3 levels. Further medical tests may be prescribed by your doctor to confirm the nature of the tumor. Reducing levels of the cancer antigen 15-3 may imply regression of the tumor. 

    The results may vary amongst laboratories.

    When should it be repeated?

    Repeat cancer antigen 15-3 blood tests can be prescribed in the following instances:

    • You can be prescribed the repeat CA 15-3 blood test to monitor the recurrence of breast cancer. This is especially amongst individuals whose stage II and stage III cancer had been successfully treated previously. This is effective in starting treatment to prevent aggravations in recurrent conditions of breast cancer.
    • To track how the body is responding to therapy for metastatic breast cancer, that is, breast cancer that is spreading to the other parts of the body. This helps in early diagnosis of the recurrence, enabling initiation of treatment at its early stages.


    The CA 15-3 tumor marker test involves a medical expert collecting blood from a patient as a sample for analysis at a laboratory. The healthcare professional selects a suitable vein, usually from the inner corner of the elbows or the hands.

    The suitability of the vein is based on whether it is a major blood vessel that is most likely to have enough blood circulation for collecting as a sample. The expert applies an antiseptic solution to clean and numb the area. Then wraps an elastic band around the arm. This serves the purpose of making the vein swell and become more visible from the skin’s surface. It also improves the chances of injecting the needle accurately.

    Next, the needle is injected to draw blood, which gets collected in the vial of the syringe. The bleeding from the puncture site is prevented with a clean cotton swab. Then the wound is covered with a bandage. The bandage accelerates the healing process and keeps infections away. This bandage can be disposed of after 10 to 15 minutes, unless advised differently by your healthcare professional.

    The entire procedure does not generally extend beyond a few minutes. The pain differs between patients, varying from a mild prick to a sharp sting. Finally, the blood sample is sent to a laboratory for microscopic evaluation.

    Learn more about screening tests for women here.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    John Paul Abrina, MD

    Oncology · Davao Doctors Hospital

    Written by Nikita Bhalla · Updated Jul 13, 2022

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