APOH and autoimmune polyendocrinopathy: In the latter, we detected anti-β2GPI IgG reactivity by four assays (in-house and commercial ELISA, CLIA, and fluorescence enzyme immunoassay), and used a modified anti-β2GPI IgG in-house ELISA with recombinant single-domain-lacking β2GPI variants to evaluate domain-dependent reactivity.<h4>Results</h4>We confirmed anti-DI, anti-DIV/DV β2GPI IgG direct reactivity in classified and non-classifiable APS in the two cohorts, and found anti-DI/anti-DIV/DV double negative (38/191, 29/105) and anti-DIV/DV single-positive (6/191, 9/105) samples.