Characteristics of patients with low serum IgE levels and selective IgE deficiency: Data from an immunodeficiency referral center.

Low immunoglobulin E (IgE) levels are defined as values below 2.5 IU/mL. Selective IgE deficiency (sIgED) refers to reduced serum IgE levels in patients with normal IgA/G/M levels. We evaluated 677 patients with low IgE levels. Recurrent infections (78.8 %), a history of allergy (27.3 %), and autoimmune/inflammatory diseases (18.3 %) are common. The primary immunodeficiency disease (PID) (n = 483, 71.3 %) diagnoses include 313 (46.2 %) patients with antibody deficiency and 119 (17.6 %) with combined immunodeficiency. Genetic pathogenic variants were present in 154 out of 207 PID patients. Within sIgED group, 23 (19.8 %) had primary immunodeficiencies. We observed a high prevalence of autoimmune/inflammatory diseases, allergies, malignancies, and PID among patients with low IgE levels. Therefore, clinicians should be vigilant when evaluating patients with low IgE levels, as this finding may indicate an underlying systemic disease or PID.