Blood Cell Counts

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Before and during treatment for breast cancer, your doctor likely will order blood cell counts. These tests check to see whether the blood has normal amounts of various types of blood cells. The cancer itself and treatments such as chemotherapy and radiation therapy can reduce the levels of important blood cells your body needs to function properly.

Blood cell counts typically measure:

  • white blood cells, which function as the immune system cells that defend your body against foreign substances and “invaders.” If you have a low white blood cell count, you have a higher risk of getting an infection.
  • red blood cells, which carry oxygen throughout the body. In addition to measuring the number of red blood cells, a test will be done to measure the level of hemoglobin, an iron-rich protein found in red blood cells that carries oxygen from your lungs to the rest of your body. (When you have low hemoglobin levels, a condition called anemia can result.) Another test will measure your hematocrit level, which is the fraction of whole blood volume that consists of red blood cells.
  • platelets, which are cells that help your blood form clots to prevent bleeding

Before treatment begins, blood cell counts may be used to determine whether you have another medical condition, such as anemia, that needs to be addressed first. Abnormal counts also could be an indication that the cancer has spread to the bone marrow (the spongy tissue inside bones where blood cells are made).

During treatment with chemotherapy, your blood cell counts will be checked before each cycle of treatment. Chemotherapy medications can significantly reduce the levels of blood cells your body should have. Radiation therapy can affect these levels as well, although to a lesser extent. Blood counts may be checked during a course of radiation, particularly if the radiation is being given to a large area or if you've just had or are still having chemotherapy.

If your counts are too low, your doctor can give you medications called growth factors to stimulate the growth of certain types of blood cells. Examples of growth factors include:

  • Procrit (chemical name: epoetin alfa), Epogen (chemical name: epoetin alfa), or Aranesp (chemical name: darbepoetin alfa) to increase red blood cell counts
  • Neumega (chemical name: oprelvekin) to increase platelet counts
  • Neupogen (chemical name: filgrastim) to boost white blood cell levels

Another option is a transfusion, which is the process of transferring healthy blood or needed blood components into your body.

After treatment, blood tests are used to look for signs of recurrence and to monitor possible side effects from medication. Counts of white blood cells (immune cells) and platelets are taken until they are back to normal. Then, your doctor will probably order blood counts only occasionally, depending on the kind of treatment you’ve had and how you are feeling.

Learn more about anemia and low white blood cell counts.

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