POSTN and eosinophilic granulomatosis with polyangiitis: Evaluation of blood eosinophil count, and sera levels of ECP, IL-5, IL-4, IgE, IgG4, ANCA, and sputum biomarkers (eosinophils, periostin, IL-8, GM-CSF) to differentiate severe asthmatic patients from the prodromal phase of EGPA.