Treatment-based approach to HESs. Algorithms are proposed for evaluation of (A) presumed HES, (B) clinically stable HES, and (C) steroid-resistant HES. *M-HES is defined for the purposes of this algorithm as HES with a genetic abnormality known to cause clonal eosinophilia or idiopathic HES with ≥4 of the following features: dysplastic eosinophils, serum B₁₂ >737.8 pM (1000 pg/mL), serum tryptase >12 ng/mL, anemia and/or thrombocytopenia, splenomegaly, bone marrow cellularity >80%, myelofibrosis, spindle-shaped mast cells >25%, or strong clinical suspicion of a myeloproliferative disorder.