Frequency of vascular and pregnancy morbidity in patients with low vs. moderate-to-high titers of antiphospholipid antibodies.

Antiphospholipid syndrome (APLS) is an autoimmune hypercoagulable syndrome characterized by thrombotic and obstetric manifestations. We sought to determine the rate of APLS feature in patients tested positive for antiphospholipid antibodies (APLA) regardless of the serum level of anticardiolipin (ACL) and/or anti-β2-glycoprotein I (β2GPI) antibodies. An inception cohort of individuals who were tested positive for ACL and/or β2GPI IgG/IgM antibody, and/or lupus anticoagulant (LAC) on two occasions of at least 12 weeks apart. A total of 243 patients were included; their mean age was 40.1 ± 15.9 years. Thrombotic vascular events occurred in 118 patients (48.5%) of the entire cohort, of which 62 patients (25.5%) suffered from an arterial event and 56 patients (23%) from thrombotic venous events. Obstetrical morbidity occurred in 106 female patients (43.6%). In our cohort, we found no difference in the frequency of thrombotic or obstetric manifestations of APLS between patients with ACL IgG/IgM of low serum antibody level (<40 U) and medium-to-high level (≥40 U) and/or anti-β2GPI IgG, IgM higher than the 99th percentile vs. lower (>20 U). We suggest that in 'real life' the diagnosis of APLS should not be excluded because of low titer of APLA.