Complete Blood Count (CBC)

A complete blood count test (CBC test)  can tell you a great deal about your patient's overall health.  The main elements that it shows information about are the red blood cells, the white blood cells, and the platelets. 

CBC test for nurses

The CBC can be used to screen a patient for certain medical conditions, show if a patient has an infection, show if a person is actively bleeding or if they are anemic, or show if a medical intervention is working correctly, just to name a few indications.  The normal values provided below are relevant for adults.  There is variation in these values based on the age of the patient.

What Is In The CBC Test?

White Blood Cells

  • White Blood Cells (Normal: 4.0 - 11.0 x10E3/uL):  This is the count of white blood cells in a person's blood sample.  A change in this number is often an identifier of an acute infection. 
  • Differential:  Usually this referred to a "CBC with diff." This includes the measurements of different types of white blood cells.  The five types that are measured are neutrophils, lymphocytes, monocytes, eosinophils, and basophils.  Providers look at the proportions of these blood cells in relation to each other to help determine whether a patient has an infection, a blood disorder, allergies, immune disorders, or other blood issues.

Red Blood Cells

  • Red Blood Cells (Normal: 4.01 - 5.47x10E6/uL):  This is the count of red blood cells in a person's blood sample. 
  • Hemoglobin (Normal: 12.0 - 16.0 gm/dL):  This is the amount of oxygen-carrying protein found in the blood sample.  When you administer one unit of blood, the patient's hemoglobin should increase by one point.  If they are actively bleeding, then you won't see a full increase by one hemoglobin point after the blood is given.
  • Hematocrit (Normal: 36-48%):  This is a percentage of the red blood cells versus the rest of the blood (plasma, platelets, etc.). The hematocrit is usually three times the amount of the hemoglobin.  For example, if a patient's hemoglobin is 9 then you would expect the hematocrit to be 9 multiplied by 3, so 27.  
  • Mean Corpuscular Volume (MCV) (Normal: 81 - 101 fL): This tells you the actual size of the average red blood cell in the sample.
  • Mean Corpuscular Hemoglobin Count (MCHC) (Normal: 31.1 - 35.5 gm/dL): The amount of hemoglobin in a single red blood cell. 
  • Red Cell Distribution (RDW) (Normal: 11.0 - 14.5%): This calculates the amount of variation there is among the red blood cell sizes.  


  • Platelet count (Normal: 150 - 400x10E3/uL):  The amount of platelets in the blood sample.  If a person is receiving heparin, it is important to look back over the past labs to see the trend of the platelet count.  If it is drastically decreasing, think about suggesting a HIT (heparin-induced thrombocytopenia) panel to see if the cause of the decreased platelets is heparin.

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