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A normal white blood cell count is 4.5–11.0 x109/L.
White blood cells (leukocytes) are types of cells in the blood and in the lymph system. There are several different kinds of white blood cells, including lymphocytes, monocytes, and granulocytes (neutrophils, eosinophils, and basophils). White blood cells are created in the bone marrow and function as part of the immune system. Many things may cause the white blood cell count to go up (leukocytosis) or down (leukopenia), such as infection, leukemia, certain other medical conditions, and certain medications.
Most commonly, white blood cell count increases when there is an infection in the body. Leukopenia can be dangerous because it means the immune system is weaker. Leukocytosis also indicates something dangerous may be going on in the body. The white blood cell count can be brought back to normal by treating the underlying cause.
What we mean by normal
In medicine, using the term “normal” can sometimes be off-putting. Saying something is “normal” implies that everything else is “abnormal.” Additionally, saying something is “normal” may not be accurate, since something that is “normal” for you may not be “normal” for somebody else. Therefore, instead of saying certain values are “normal,” alternative terminology may be to say that these values are “healthy” or “within the reference range.”
Additionally, some values have well-defined cutoffs, while others do not. For example, when looking at hemoglobin A1c levels, a value of 6.5 or greater is always diagnostic of diabetes. On the other hand, when looking at testosterone levels, some use cutoffs of 270–1,070 ng/dL while others use cutoffs of 300–1,000 ng/dL.
The information above represents values that are commonly used as cutoffs. However, depending on the specific source you’re looking at or the laboratory you go to, their values may be a little different.
Dr. Tzvi Doron is Board Certified in Family Medicine by the American Board of Family Medicine and is Ro's Chief Clinical Officer.