Patients with positivity for antiphospholipid antibodies (aPLs) who were enrolled in an international registry, the Antiphospholipid Syndrome (APS) Alliance for Clinical Trials and International Networking (APS ACTION) clinical database and repository, were assessed, overall and by clinical and laboratory subtypes, for their baseline characteristics.

• In the present study, researchers assessed 804 aPL-positive patients (mean age: 45 ± 13 years; 74% females; 68% White; 36% with other systemic autoimmune diseases).

• Classification revealed 80% as having APS (with 55% having thrombotic APS, 9% obstetric APS, and 15% thrombotic APS/obstetric APS).

• In the overall cohort, vascular thrombosis was recorded in 71%, obstetric morbidities were recorded in 50% with a history of pregnancy, and at least one non-criteria manifestation was observed in 56%.

• Among those with three aPLs tested (n = 660), 42% were triple aPL–positive.

• While single–, double–, and triple aPL–positive subgroups had similar frequencies of vascular, obstetric, and non-criteria events, these events were lowest in the single aPL subgroup, which consisted of aCLs or anti-β2GPI only.

• Overall findings from this multicenter international cohort study suggest heterogeneity of aPL-related clinical manifestations and laboratory profiles.

• Overall there may be a major contribution of lupus anticoagulant [LAC] to clinical events within single aPL positivity.

• Future prospective analyses, using standardized core laboratory aPL tests, will aid in clarifying aPL risk profiles and enhance risk stratification.