What is a complete blood count (CBC)?

A complete blood count (also known as CBC) is a test that provides information about several features and components of your blood, including:

  • Red blood cells – cells that carry oxygen to your body
  • White blood cells – cells that fight infection
  • Hb or Hbg (hemoglobin) – number of red blood cells you have
  • Hct (hematocrit) – measures how much of your blood is made up of red blood cells
  • Platelets – platelets are pieces of a whole cell that help clots form to stop bleeding

Why is a complete blood count done?

A CBC can be done for many reasons. Your doctor or nurse might order this test as part of your annual well check-up. Also, if you have already been diagnosed with a certain disease or if you are at high-risk for a certain disease due to family history, your doctor or nurse might check your CBC regularly to make sure your blood counts are okay.

The results of the test can show a variety of health conditions. Some common examples are:

  • Anemia – too few red blood cells.
  • Polycythemia –too many red blood cells.
  • Bleeding or clotting disorders – If your blood makes too many or too few platelets, you might have a bleeding or clotting disorder
  • Problems with the body's infection-fighting system if your white blood cell level is low

What to expect during a CBC

A CBC is a pretty simple test and takes only a few minutes. A lab tech or nurse will take a sample of blood by inserting a needle into a vein in your arm. It will be sent to the lab for review and you can go back to your normal routine. The doctor who ordered your test will call to discuss any concerns with the results.

Common reasons this test is performed

  • Identify signs of anemia
  • Identify signs of leukemia
  • Evaluation of a condition you already have
  • Check for a health issue to explain weakness, fever, feeling tired or bruising
  • Check if medications you are taking are affecting your blood
  • Routine yearly check-up

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