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 beta 2-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, 130-282% vs controls; median, 247%; range, 217-283%; P < .0001) and elevated levels of anti-domain I immunoglobulin (Ig) G (optical density: median, 0.056; range, 0.021-0.489 vs median, 0.042; range, 0.020-0.323; P = .002). Those in the lowest tertile of AnxA5 anticoagulant ratios had an odds ratio for Obs-APS of 58.0 (95% confidence interval, 3.3-1021.5). 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 beta 2-glycoprotein I and identifies a subset of women with histories for Obs-APS.