Complete Blood Count

While watching your favorite medical tv drama you may have heard the letters CBC. Or maybe your physician mentioned getting “blood counts,” What does this mean exactly?   

CBC stands for a complete blood count. This laboratory test requires blood to be drawn from a vein, usually in the arm or hand.  It is one of the most commonly drawn lab tests and is often a part of a routine or annual blood work. The normal values on a CBC vary by age and sex. CBC has many uses including screening for anemia, looking for signs of an infection, and as part of a workup of cancer.   ​

So now you’ve had your CBC drawn, but what does it tell the healthcare provider? Our blood is made of three types of blood cells: white blood cells, red blood cells, and platelets. Below we will review some of the results of a CBC. 


White Blood Cells

White blood cells primarily help to fight infections.  Generally, the white blood cell count will be higher than normal during infections and return to normal when the infection resolves. If the bone marrow is not working properly, like in aplastic anemia, the white blood cell count may be low. Leukemia is a cancer of the white blood cells which typically results in a very high level of white blood cells on the CBC.  Elevated white blood cell count is called leukocytosis and the low white blood cell count is called leukopenia. 



Hemoglobin is a protein in our red blood cells (RBC) that carries oxygen to all the tissues of the body. Low hemoglobin is called anemia while elevated hemoglobin can be called polycythemia or erythrocytosis. Anemia may result from a variety of causes including iron deficiency, blood loss, or bone marrow failure. Polycythemia is much rarer than anemia.  



The hematocrit is sometimes called the packed cell volume. It is the volume percentage of red blood cells in the blood. 



Platelets are blood cells that help us stop bleeding. A low platelet count is called thrombocytopenia and an elevated platelet count is called thrombocytosis. 


Mean Corpuscular Volume

Also known as MCV. This is a measurement of the size of the RBC. In conditions like iron deficiency anemia, the hemoglobin and the MCV will be low. Alternatively, folate or vitamin B12 deficiency can result in an MCV that is higher than normal. 


Mean Corpuscular Hemoglobin Concentration

Also known as MCHC. This is a measurement of whether there is enough hemoglobin in the RBC. Most commonly, hereditary spherocytosis causes a higher than normal MCHC.  


Red Cell Distribution Width

Abbreviated RDW. RDW represents the amount of variation in size in the red blood cells. A normal value would indicate that all the red blood cells are similar in size. A high RDW indicates a lot of variation in the size of the red blood cells. In iron, folate, or vitamin B12 deficiency anemia, the RDW is often elevated.   



The differential refers to the assorted types of WBC. There are 5 types of WBC: neutrophils also called segments, lymphocytes, monocytes, eosinophils, and basophils. Neutrophils help fight bacterial infections.  Lymphocytes fight viral infections. Monocytes fight many types of infections. Eosinophils are involved in allergic reactions and parasite infections. Basophils are the hermit of the WBC, with very few in circulation. They are involved in inflammatory reactions.  

Review the Results With Your Doctor

Just because one of the values on the CBC are marked as abnormal (usually high or low), this doesn’t necessarily mean something is “wrong”. If you have concerns, you should discuss it with your healthcare provider. Hopefully, this helped you understand the CBC a little better and next time your healthcare provider hands your CBC results to you, it won’t just look like alphabet soup.

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