The complete blood count (CBC) is a blood test that is used to diagnose a wide variety of conditions, including anemia, infection, cancer of the blood (leukemia) and to also determine the general health. 

A complete blood count (CBC) test shows some of the components and attributes of blood, including: 

  • Red blood cells
  • White blood cells that combat infections 
  • Hemoglobin, an oxygen-carrying protein in red blood cells
  • Hematocrit, the proportion of red blood cells in your blood to the fluid part or plasma
  • Platelets that assist in blood coagulation

As seen in a full blood count, irregular increases or decreases in cell counts can mean that you have an underlying medical condition that calls for further examination. 


  • CBC for adults. A lab technician, typically from the inside of the elbow or from the back of your hand, will draw blood from a vein. It only takes a few minutes for the test.
  • CBC for infants. A nurse will usually sterilize the heel in the foot of infants and use a lancet or a small needle to prick the area. The nurse will then squeeze the heel gently and collect a small amount of blood for testing in a vial.


Usually, a full blood count is not a conclusive screening examination. Results outside of the usual range may or may not require follow-up, depending on the explanation that the doctor ordered this examination. Your doctor will need to look at the findings of a CBC test along with the results of other blood testing, or it may require additional checks.

For example, if you are otherwise stable and have no signs or symptoms of disease, outcomes on a full blood count marginally above the normal range may not be a cause for concern, and follow-up may not be necessary. The findings of a full blood count above the normal range may suggest a need to change your care plan if you are receiving cancer therapy. 

In certain cases, your doctor may refer you to a physician who specializes in blood disorders if your findings are substantially above or below the normal range (hematologist).

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