Eosinophilia is not a rare finding in clinical practice, and often poses problems in terms
of etiologic research and differential diagnosis. Peripheral eosinophilia is defined by a blood eosinophil
count > 500 cells/μL. It is classified into mild (500-1500 cells/μl), moderate (1500-5000
cells/μl) and severe for an eosinophil count > 5000 cells /μl. The term "hypereosinophilia” defines
a condition characterized by a blood eosinophil count >1500 cells/μl in at least two consecutive
tests made with a minimum of a 4-week interval. The causes of eosinophilia are various, and can be
summarized by the acronym “APLV” which refers to Allergic disorders, Parasitic infections, Leukemia/
Lymphomas (and solid tumors) and Vasculitis-Immunodeficiency diseases, with allergic
disorders and parasitic infections representing the most commonly identified causes. Allergic disorders
are usually associated with mild eosinophilia, whereas values >20.000 cell/μl are highly
suggestive for myeloproliferative disorders. Eosinophils may also be directly responsible for organ
damage, mainly at cardiac, pulmonary and cutaneous level, deriving from the release of the granule
products, of lipidic mediators and cytokines. Therefore, in the physician’s approach to a patient
with persistent hypereosinophilia, it is also important to investigate the presence of organ involvement.
In this review, we propose a diagnostic algorithm for children presenting with either blood
eosinophilia or hypereosinophilia. This algorithm focuses on the patient’s history and clinical manifestations
as the first step and the level and persistence of blood eosinophilia as the second, and this
can help the physician to identify patients presenting with an elevated blood eosinophil count that
need further laboratory or instrumental investigations.
Keywords: Allergy, asthma, atopic dermatitis, DRESS, eosinophil, eosinophilia, hypereosinophylic syndromes, parasites.
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