1. Immunogenicity testing of biologic products relies entirely on the design and execution of the assays used, making it impossible to directly compare reported immunogenicity rates between products unless a head-to-head clinical study is conducted. 2. Multiple factors influence reported immunogenicity rates, including the assay format, sensitivity, controls, and clinical study design. The choice of assay cut-off also impacts the rate of samples deemed positive or negative. 3. Even in head-to-head clinical studies, biosimilar companies may report only relative immunogenicity compared to the reference product due to differences in assay methodology and validation between companies. Direct comparison of rates is generally not possible without identical assay methodology.