Medical Definition of Eosinophilia

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Reviewed on 12/21/2018

Eosinophilia: An abnormally high number of eosinophils in the blood. Normally, eosinophils constitute 1 to 3% of the peripheral blood leukocytes, at a count of 350 to 650 per cubic millimeter. Eosinophilia can be categorized as mild (less than 1500 eosinophils per cubic millimeter), moderate (1500 to 5000 per cubic millimeter), or severe (more than 5000 per cubic millimeter).

In areas of the world where parasitic diseases are common, they are the usual cause of eosinophilia. In developed nations, eosinophilia is most often due to allergy or, less often, a drug reaction. There are numerous other causes of eosinophilia, but individually they are quite uncommon.

Eosinophilia may be primary or secondary. In primary eosinophilia, the increased production of eosinophils is due to an abnormality in a hematopoietic stem cell as, for example, in eosinophilic leukemia. In secondary eosinophilia, the increased production of eosinophils is a reactive process driven by cytokines, as is the case in allergy.

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Reviewed on 12/21/2018