Non-syndromic elevated IgE

I have read the article titled, "Non-syndromic hyper-IgE in children: A practical approach", by Castagnoli et al with great interest. 1This exciting review article addresses elevated IgE levels not associated with syndromic disorders.While reading this interesting article, 1 we observed some omissions in definitions and concepts that made certain points difficult to understand.Clarifying these issues would help readers better understand this review article. 1 Hyper-IgE, as mentioned in the article, 1 is generally defined as serum IgE levels exceeding 2.000 IU/mL.However, for non-syndromic hyper-IgE in children, should we consider values above 2.000, or values above the upper limit of the range, or values above +2SD?When searching PubMed for "non-syndromic hyper-IgE," nothing comes up.This needs to be clearly established.