Mold Exposure and Eosinophilia

Introduction to Immunologic Mechanisms

Elevated IgG antibodies to mold indicate prior exposure but do not directly cause eosinophilia; however, concurrent mold exposure can trigger IgE-mediated allergic responses or hypersensitivity pneumonitis that independently elevate eosinophils through distinct immunologic pathways 1, 2

Blood eosinophilia (≥500 cells/μL) occurs in allergic conditions, including mold-induced asthma and allergic rhinitis, representing the most common cause of mild eosinophilia 3
Hypersensitivity pneumonitis from mold involves non-IgE immune mechanisms that can produce eosinophilia through cell-mediated immunity 4
Serum antigen-specific IgG/IgA testing should not be used alone to confirm or rule out hypersensitivity pneumonitis, as these antibodies indicate exposure but not disease 4

Persistent eosinophilia ≥1500 cells/μL for >3 months requires hematology referral to exclude hypereosinophilic syndrome or myeloid neoplasms 3
Blood eosinophilia with tissue eosinophilia (≥15 eosinophils/high-power field) may indicate allergic bronchopulmonary aspergillosis (ABPA), which presents with elevated Aspergillus-specific IgE (not just IgG), total IgE ≥500 IU/mL, and blood eosinophils ≥500 cells/μL 1, 2