Complete Blood Count (CBC)

Medical Author: Siamak Nabili, MD, MPH
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

• What is the complete blood count test (CBC)?
• How is the complete blood count test (CBC) done?
• What are the components of the complete blood count (CBC)?
• What are values for a complete blood count (CBC)?
• What are the functions of the cells in a complete blood count (CBC)?
• What is the complete blood count (CBC) used for?

What is the complete blood count test (CBC)?

The complete blood count (CBC) is one of the most commonly ordered blood tests. The complete blood count is the calculation of the cellular (formed elements) of blood. These calculations are generally determined by special machines that analyze the different components of blood in less than a minute.

A major portion of the complete blood count is the measure of the concentration of white blood cells, red blood cells, and platelets in the blood.

How is the complete blood count test (CBC) done?

The complete blood count (CBC) test is performed by obtaining a few milliliters (one to two teaspoons) of blood sample directly form the patient. It can be done in many settings including the doctor's office,  laboratories, and hospitals. The skin is wiped clean with an alcohol pad, and then a needle is inserted through the area of cleansed skin into to patient's vein (one that can be visualized from the skin.) The blood is then pulled from the needle by a syringe or by a connection to a special vacuumed vial where it is collected. This sample is then taken to the laboratory for analysis.

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