Resistance to annexin A5 anticoagulant activity in women with histories for obstetric antiphospholipid syndrome

Objective: The objective of the study was to investigate whether resistance to annexin A5 anticoagulant activity (AnxA5) occurs in women with histories for obstetric complications of antiphospholipid syndrome (Obs-APS) and whether this correlates with antibody recognition of domain 1 of β2-glycoprotein. Study Design: One hundred thirty-six women with antiphospholipid antibodies, including 70 with histories for Obs-APS and 30 controls, were investigated. Results: Women with Obs-APS showed resistance to AnxA5 activity (median, 216%; range, 130282% vs controls; median, 247%; range, 217283%; P <.0001) and elevated levels of anti-domain I immunoglobulin (Ig) G (optical density: median, 0.056; range, 0.0210.489 vs median, 0.042; range, 0.0200.323; P =.002). Those in the lowest tertile of AnxA5 anticoagulant ratios had an odds ratio for Obs-APS of 58.0 (95% confidence interval, 3.31021.5). There was an inverse correlation between levels of annexin A5 anticoagulant activity and anti-domain I IgG. Conclusion: Resistance to AnxA5 anticoagulant activity is associated with antibody recognition of domain I of β2-glycoprotein I and identifies a subset of women with histories for Obs-APS.