Merck Manual

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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 Aug 2021
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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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