How is a complete blood count test performed?

In order to perform the CBC panel of tests, blood must be drawn from the patient. In adults, the blood is usually obtained from a vein in the arm. In infants, the blood is usually taken from the heel.

What should I do to prepare for a complete blood count test?

You do not have to do anything to prepare for a CBC.

What other measurements are shown by a complete blood count?

  • Hematocrit (HCT): the percentage of red blood cells in the total volume of blood
  • Platelet count: the number of platelets in thousands per cubic milliliter (K/ml3) of blood. Platelets form clots in order to stop bleeding.
  • Mean platelet volume (MPV): the average size of platelets. This is important because new platelets are bigger than older ones, and a higher MPV indicates a higher platelet output.
  • Mean corpuscular hemoglobin (MCH): the average amount of hemoglobin in a red blood cell.
  • Mean corpuscular hemoglobin concentration (MCHC): the average concentration of hemoglobin in a red blood cell. The MCHC gives the health care provider an impression of the pallor of the cell; for example, very pale to very dark red. The degree of paleness may help in establishing a diagnosis.
  • Mean corpuscular volume (MCV): the average size of red blood cells. "Macrocytic" describes a state in which red blood cells are bigger than normal; "microcytic" refers to the state in which red blood cells are smaller than normal. The average size of the red blood cells may help in establishing a diagnosis.
  • Red blood cell distribution width (RDW): the amount of variation in the size of the red blood cells.

Last reviewed by a Cleveland Clinic medical professional on 09/09/2014.


  • Lab Tests Online. Complete Blood Count Accessed 9/19/2014.
  • National Heart, Lung, and Blood Institute. Types of Blood Tests Accessed 9/19/2014.
  • National Institutes of Health. Understanding the Complete Blood Count (CBC) and Common Blood Deficiencies Accessed 9/19/2014.

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