Complete Blood Count: Why It's Used and What It Detects

What Can a CBC Tell You?

Blood Tests
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A complete blood count (CBC) is a test that measures the numbers, types, and health of the cells in the blood. A physician will often order a CBC as part of an annual physical, to help guide further testing, diagnose a range of conditions, or to monitor your health while taking certain medications. 

A CBC can help diagnose blood diseases such as leukemia; determine how well your body is responding to and handling various medications or cancer treatments; diagnose types and severity of anemia; and decide on further treatments that may be needed to keep you healthy, such as a medication to boost your blood cell counts.

What Does a CBC Measure?

A complete blood count test measures various components and characteristics of blood, including:

  • The number of red blood cells, which transport oxygen throughout the body
  • The number of white blood cells, which help defend the body against infections and cancer as well as play a role in allergies and inflammation
  • The total amount of hemoglobin, an oxygen-carrying protein in the blood
  • Hematocrit, the percentage of total blood volume that consists of red blood cells 
  • The number of platelets, cell components that are critical for normal blood clotting

In addition, a CBC provides information about:

  • Mean corpuscular volume, or MCV: Average size of red blood cell 
  • Mean corpuscular hemoglobin, or MCH: Hemoglobin amount per red blood cell
  • Mean corpuscular hemoglobin concentration, or MCHC: The amount of hemoglobin compared to the size of the red blood cell (hemoglobin concentration) 

    How to Interpret Results

    A physician or other trained healthcare professional will be able to look at the various components of the CBC, and analyze and interpret their meaning. Depending on the results, the ordering physician may be able to diagnose the cause of symptoms. For example, fatigue can result from anemia, which develops when blood is deficient in healthy red blood cells or hemoglobin.

    In other cases, a CBC may indicate that more testing is necessary. 

    Normal blood counts vary depending on whether the patient is a child or adult as well as at various levels of altitude. Generally, normal results are:

    RBC count:

    • Male: 4.7 to 6.1 million cells/mcL
    • Female: 4.2 to 5.4 million cells/mcL

    WBC count:

    • 4,500 to 10,000 cells/mcL


    • Male: 40.7 to 50.3%
    • Female: 36.1 to 44.3%


    • Male: 13.8 to 17.2 gm/dL
    • Female: 12.1 to 15.1 gm/dL

    Red blood cell indices:

    • MCV: 80 to 95 femtoliter
    • MCH: 27 to 31 pg/cell
    • MCHC: 32 to 36 gm/dL

    Platelet count:

    • 150,000 to 450,000/dL

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