The Epidemiology of Antiphospholipid Syndrome: A Population‐Based Study

<jats:sec><jats:title>Objective</jats:title><jats:p>To estimate the annual incidence and prevalence of and frequency of mortality associated with antiphospholipid syndrome (<jats:styled-content style="fixed-case">APS</jats:styled-content>).</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>An inception cohort of patients with incident <jats:styled-content style="fixed-case">APS</jats:styled-content> in 2000–2015 from a geographically well‐defined population was identified based on comprehensive individual medical records review. All cases met the 2006 Sydney criteria for <jats:styled-content style="fixed-case">APS</jats:styled-content> (primary definition) or had a diagnosis of <jats:styled-content style="fixed-case">APS</jats:styled-content> confirmed by physician consensus (secondary definition). Levels of lupus anticoagulant, IgM and IgG anticardiolipin antibodies, and anti–β2‐glycoprotein I antibodies were tested in a centralized laboratory. Incidence rates were age‐ and sex‐adjusted to the 2010 <jats:styled-content style="fixed-case">US</jats:styled-content> white population. Prevalence estimates were obtained from the incidence rates, assuming that there was no increased mortality associated with <jats:styled-content style="fixed-case">APS</jats:styled-content> and that migration in or out of the area was independent of disease status.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Among this cohort in 2000–2015, 33 cases of incident <jats:styled-content style="fixed-case">APS</jats:styled-content>, as defined by the Sydney criteria, were identified (mean age of patients 54.2 years; 55% female, 97% white). The annual incidence of <jats:styled-content style="fixed-case">APS</jats:styled-content> in adults ages ≥18 years was 2.1 (95% confidence interval [95% <jats:styled-content style="fixed-case">CI</jats:styled-content>] 1.4–2.8) per 100,000 population. Incidence rates were similar in both sexes. The estimated prevalence of <jats:styled-content style="fixed-case">APS</jats:styled-content> was 50 (95% <jats:styled-content style="fixed-case">CI</jats:styled-content> 42–58) per 100,000 population, and was similar in both sexes. Six patients (18%) had a concurrent diagnosis of systemic lupus erythematosus. The most frequent clinical manifestation was deep vein thrombosis. The overall frequency of mortality among patients with <jats:styled-content style="fixed-case">APS</jats:styled-content> was not significantly different from that in the general population (standardized mortality ratio 1.61, 95% <jats:styled-content style="fixed-case">CI</jats:styled-content> 0.74–3.05).</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p><jats:styled-content style="fixed-case">APS</jats:styled-content> occurred in ~2 persons per 100,000 population per year. The estimated prevalence was 50 per 100,000 population. Overall mortality was not notably different from that observed in the general population.</jats:p></jats:sec>