Table 1.

Classification of hypereosinophilia

Proposed terminology	Pathogenesis/definition
Hereditary (familial) hypereosinophilia	Pathogenesis unknown; familial eosinophilia.
Hypereosinophilia of undetermined significance	No underlying cause of hypereosinophilia, no family history.  No symptom of hypereosinophilia.
Primary (clonal/neoplastic) hypereosinophilia	Underlying stem cell, myeloid or eosinophilic neoplasm (WHO criteria).
Secondary (reactive) hypereosinophilia	Underlying condition/disease in which eosinophils are non-clonal cells.  Hypereosinophilia is triggered by cytokines.

Note: Adapted from J Allergy Clin Immunol, 130(3), Valent P, Klion AD, Horny HP, et al. Contemporary consensus proposal on criteria and classification of eosinophilic disorders and related syndromes, 607–612.e9. Copyright (2012), with permission from Elsevier.⁷

Abbreviation: WHO, World Health Organization.