A CBC measures your red and white blood cells and your platelets. Although this blood test gives doctors a wide range of important medical information, it can’t detect breast cancer.

A complete blood count (CBC) is a common part of breast cancer treatment. Doctors typically order a CBC before treatment to get an idea of your baseline blood counts.

Doctors also use CBCs during treatment to ensure your blood cell levels aren’t dropping. The CBC will alert doctors if levels are too low and you’ll be treated before you experience side effects.

In this article, we take a look at how CBCs are used before and during breast cancer treatment, and the tests doctors use to detect and diagnose breast cancer.

A complete blood count (CBC) measures the numbers and health of your white blood cells, red blood cells, and platelets. It’s an important marker of your health, and it’s frequently done before cancer treatments are started.

Doctors may also order additional blood tests to help stage your cancer and learn more about your genetics. For example:

  • Blood chemistry tests: These tests look at the levels of certain chemicals in your blood. They’re a good measure of how your organs are functioning and may be used to help stage your cancer.
  • Tumor marker tests: These tests look for the presence of cancer antigens in the blood. A cancer antigen is a protein found in cancer cells. However, cancer isn’t the only thing that can cause these antigens, and not everyone with breast cancer will have cancer antigens. In breast cancer, cancer antigens include cancer antigen 15-3 (CA15-3) and carcinoembryonic antigen (CEA).

Symptoms of cancer, and treatments such as radiation and chemotherapy, can affect the levels of blood cells in your body. Checking before treatment begins gives doctors an idea of your baseline. They check again during your treatments to monitor your blood count levels.

If chemotherapy or radiation is causing your level of red blood cells, white blood cells, or platelets to drop, you can receive medications alongside your treatments to help prevent side effects of low blood counts, such as anemia.

After treatment ends, a CBC can help doctors get a look at your overall health and make sure you’re not experiencing any negative reactions to medications.

A CBC can’t detect or diagnose breast cancer, but there are tests that will confirm a diagnosis. Often, a physical exam of breast tissue and a review of your medical history will be the first step. From there, your doctor might recommend testing, including:

  • Diagnostic mammogram: A diagnostic mammogram is an imaging test that creates detailed images of the breast.
  • Ultrasound: An ultrasound uses sound waves to create close-up images that help doctors determine if an abnormality in breast tissue is a tumor or a cyst.
  • Biopsy: A biopsy is the only way to confirm a diagnosis of breast cancer. A biopsy procedure involves removing a small amount of tissue from the lump or abnormal area and then having that tissue tested for cancer in a lab. Typically, a biopsy is an outpatient procedure, however, sometimes surgical biopsies that remove the entire lump are performed.
  • Lymph node biopsy: If your doctor suspects your cancer has spread to your lymph nodes, they might be surgically removed and then tested for cancer.

The exact requirements for breast cancer screening depend on your overall risk and your age.

According to the U.S. Preventative Services Task Force (USPSTF), women under the age of 50 should have a discussion with their doctor about the pros and cons of every-other-year mammogram screenings between the ages of 40 and 49.

Starting at age 50, the USPSTF recommends mammogram screening every 2 years for those at average risk.

Screenings should continue as long as the person remains in good health. However, some people who are at a higher risk, such as people who have the BRCA1 and BRCA2 genes are advised to begin yearly screenings earlier.

Read more about breast cancer screening recommendations here.

Can other cancers be detected in a CBC?

Most cancers are detected when imaging tests, such as CT scans or MRIs, spot tumors or signs of organ damage.

However, blood cancers, such as leukemia and lymphoma raise white blood cell counts and can be detected in a CBC. Other tests will still be needed to confirm a diagnosis.

Why do doctors typically order a CBC?

A CBC is a common test that can help doctors get a snapshot of your overall health. It can also be used to look for:

  • leukemia
  • lymphoma
  • anemia
  • infection
  • the effects of certain medications

What’s included in a CBC?

A CBC measures the components of your blood. This includes:

  • Red blood cells: Red blood cells transport oxygen throughout your body.
  • White blood cells: Your body uses white blood cells to fight infection.
  • Hemoglobin: Hemoglobin are proteins inside your red blood cells.
  • Hematocrit: Hematocrit is the fluid, or plasma in your red blood cells.
  • Platelets: Platelets are what allow your blood to clot.

What are normal CBC values?

The typical values on a CBC are listed below.

Blood componentsPeople assigned male at birthPeople assigned female at birth
red blood cell count4.35–5.65 trillion cells/L3.92–5.13 trillion cells/L
hemoglobin13.2–16.6 grams/dL11.6–15 grams/dL
white blood cell count3.4–9.8 billion cells/L3.4–9.8 billion cells/L
platelet count135 to 317 billion/L 157–371 billion/L

A complete blood count (CBC) is a test that can help doctors get a picture of your overall health. It’s often used to check for infections, and it can help detect some blood cancers.

Although a CBC can’t detect breast cancer, it’s used before and during breast cancer treatment. Chemotherapy and radiation can destroy blood cells. A CBC can check blood cell levels. If your levels drop during treatment, medication can help bring them up so that you don’t experience side effects.

After treatments are finished, a CBC is a good marker of whether you’ve returned to your baseline, and a good way to ensure you’ve not experienced any negative reactions to medications.