Treatment-based approach to the patient with presumed HES. *Four or more of the following: 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%.