Table 2.

Definitions of hypereosinophilic syndrome

WHO definition of HES	Consensus definition
AEC >1.5 × 109/L for greater than 6 months	AEC >1.5 × 109/L on 2 examinations at least 1 month apart and/or tissue HE
Evidence of end-organ manifestations	Organ damage and/or dysfunction attributable to tissue HE and exclusion of other conditions as a major reason for organ damage
“Idiopathic”—exclusion of reactive HE, lymphocytic variant HES, CEL-NOS, WHO-defined malignancies, eosinophilia-associated MPNs, or AML/ALL with rearrangements of PDGFRA, PDGFRB, FGFR1, or PCM1-JAK2	Includes multiple clinical classifications, including idiopathic, primary (clonal/neoplastic), secondary (presumed cytokine driven—including lymphocytic variant), and hereditary

ALL, acute lymphocytic leukemia; AML, acute myeloid leukemia; CEL-NOS, chronic eosinophilic leukemia-not otherwise specified; MPN, myeloproliferative neoplasm; WHO, World Health Organization.