Antibodies to Domain 4/5 (Dm4/5) of β2-Glycoprotein 1 (β2GP1) in different antiphospholipid (aPL) antibody profiles

Abstract Background Determination of the three recommended tests for the diagnosis of antiphospholipid syndrome [Lupus Anticoagulant (LA), anticardiolipin (aCL) and anti β2-Glycoprotein 1 (aβ2GP1) antibodies] allow physicians to allocate patients into classification (risk) categories. Objectives To measure antibodies of IgG isotype directed towards Domain 4/5 (Dm4/5) of β2GP1. Patients/Methods. In this cross-sectional study we measured IgG aβ2GP1-Dm4/5 in a group of individuals positive for IgG aβ2GP1 and classified as triple (LAC +, IgG aCL +, IgG aβ2GP1 +, n = 32), double (LAC-, IgG aCL +, IgG aβ2GP1 +, n = 23) or single positive (LA-, IgG aCL-, IgG aβ2GP1 +, n = 10). Results Geometric mean and standard deviation of IgG aβ2GP1 values expressed as Chemiluminescent Units (CU) in triple, double, single positive groups and in 40 healthy individuals were 1795 ± 783, 321 ± 181, 29 ± 8 and 5.0 ± 1.0, respectively (ANOVA p  Conclusion Mean level of IgG aβ2GP1-Dm4/5 is higher in single positive group. There is no association between positivity to IgG aβ2GP1-Dm4/5 and thromboembolic events.