Antiphospholipid Syndrome Alliance For Clinical Trials and International Networking (APS ACTION) is an international research network devoted to conducting well-designed clinical trials in persistently antiphospholipid antibody (aPL)–positive patients. One of the first needs of APS ACTION was to know the true aPL frequency in patients with pregnancy morbidity (PM), stroke (ST), myocardial infarction (MI), and deep venous thrombosis (DVT).
The search for “aPL” and multiple keywords regarding the outcomes of interest was completed in PubMed. The median frequency for positive aPL tests (lupus anticoagulant, antibody against cardiolipin [aCL], and antibody against β(2)-glycoprotein I [anti-β(2)GPI]) was calculated for each outcome and was used to estimate the overall aPL frequency.
Based on the analysis of 120 full-text papers, the overall aPL frequency was estimated as 6% for PM, 13.5% for ST, 11% for MI, and 9.5% for DVT. Limitations of the literature were that 60% of the papers were published before 2000, all 3 criteria aPL tests were performed in only 11% of the papers, 36% of papers used a low-titer aCL cutoff, anti-β(2)GPI cutoff was quite heterogeneous, aPL confirmation was performed in only one-fifth of papers, and the study design was retrospective in nearly half of the papers.
It is difficult to determine the frequency of a “clinically significant aPL profile” in patients with aPL-related clinical outcomes due to the lack of robust data. Our best estimates of the incidence of aPL-associated events should be confirmed with appropriately designed population studies.