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High White Blood Cell Count

(Leukocytosis)

By

Mary Territo

, MD, David Geffen School of Medicine at UCLA

Last full review/revision Aug 2021| Content last modified Sep 2022
CLICK HERE FOR THE PROFESSIONAL VERSION

White blood cells (leukocytes) are an important part of the body’s defense against infectious organisms and foreign substances (the immune system White blood cells ). The number of white blood cells (white cell count) is normally less than 11,000 cells per microliter of blood (11 × 109 per liter).

The most common cause of an increase in the white blood cell count is

  • The normal response of the body to an infection

Other causes include

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