Dear Editor, we thank Dulak and Trzciński for their insightful and pertinent comments on our observation about serum IgG4 levels predicting mortality in hospitalized patients affected by Coronavirus Disease 2019 (COVID-19) [1,2]. In particular, we agree that serum IgG4 levels may vary significantly in healthy individuals and in various inflammatory and allergic diseases [3,4]. We also recognize, as acknowledged in the discussion, that the limited number of patients included in the study does not allow definitive conclusions about the practical utility of our findings.