Background/Purpose: The epidemiology of definite antiphospholipid syndrome (APS) in the general population has not been described. A recent meta-analysis (Andreoli L, et al. Arth Care Res 2013;65:1869-73) concluded that it was difficult to determine the frequency of a “clinically significant antiphospholipid (aPL) profile” in patients with aPL-related clinical outcomes due to the lack of robust data; only 4% of the studies had the current cutoff values for anticardiolipin antibodies (aCL) and less than one fifth of them had confirmation after 6-12 weeks. This study aimed to characterize the epidemiology of definite APS based on the 2006 updated international consensus (Sydney) classification criteria.

Methods: An inception cohort of patients with incident APS in 2000-2015 in a geographically well-defined population were identified based on comprehensive individual medical record review. All cases met the definite 2006 Sydney consensus APS criteria, including the laboratory and clinical criteria as well as laboratory confirmation after 12 weeks. Lupus anticoagulant, IgM and IgG aCL and anti-β2 glycoprotein-1 antibodies were tested in a centralized lab (cutoff >40 GPL/MPL). Incidence rates were age and sex adjusted to the US white 2010 population. Prevalence estimates were obtained from the incidence rates assuming no increased mortality associated with APS and assuming migration in/out of the area was independent of disease status.

Results: In 2000-2015, 33 cases of incident APS were identified (mean age 54.2 years, 55% female; 97% Caucasian). The annual incidence of definite APS was 2.0 per 100,000 population aged ≥ 18 years (95% confidence interval [CI]: 1.1-3.1 per 100,000). Incidence rates were similar in both sexes (2.1 per 100,000 population in females and 2.0 per 100,000 population in males). The peak incidence was observed in those who were older than 75 years. Significant changes in incidence rates over time were not observed. Six (18%) of the patients had a concurrent diagnosis of systemic lupus erythematosus. Three (17%) patients had obstetric manifestations. During a median follow-up of 8.8 years, 7 patients died (84% survival at 10 years after APS incidence; 95% CI: 69-100%). The overall mortality of patients with APS was not significantly different from the general population (standardized mortality ratio: 1.14; 95% CI, 0.46-2.64). The estimated prevalence of APS adjusted to the US white 2010 population was 50 per 100,000 (95% CI: 42-58) and was similar in both sexes (51/100,000 for females and 48/100,000 for males). Based on this and US census data, an estimated 119,300 persons in the US were affected by APS in 2015.

Conclusion: Results from this first ever population based study revealed that definite APS occurred in about 2 persons per 100,000 per year. The estimated prevalence is 50 per 100,000. Overall mortality was not different from the general population. The prevalence of APS in the same population was at least as common as SLE (Jarukitsopa, et al. Arth Care Res 2015;67:817-28).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/epidemiology-of-antiphospholipid-syndrome-a-population-based-study/