Complete Blood Count (CBC): About Your Child's Test

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What is it?

A complete blood count (CBC) is a blood test that gives important information about blood cells, especially red blood cells, white blood cells, and platelets.

Why is this test done?

A CBC may be done as part of a regular physical exam. There are many other reasons that a doctor may want this blood test, including to:

  • Find the cause of symptoms such as fatigue, weakness, fever, bruising, or weight loss.
  • Find anemia or an infection.
  • See how much blood has been lost if there is bleeding.
  • Diagnose diseases of the blood, such as leukemia or polycythemia.

How do you prepare for the test?

Your child does not need to do anything before having this test.

How is the test done?

A health professional uses a needle to take a blood sample, usually from the arm.

A heel stick is used to get a blood sample from a baby. The baby's heel is poked, and several drops of blood are collected. Your baby may have a tiny bruise where the heel was poked.

What happens after the test?

  • Your child will probably be able to go home right away.
  • Your child can go back to his or her usual activities right away.

Where can you learn more?

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The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.