Background/Purpose: The APS ACTION Registry was created to study the natural course of disease over 10 years in persistently antiphospholipid antibody (aPL)-positive patients with or without other systemic autoimmune diseases (SAID). The primary objective of this study was to update the incident first and recurrent thrombosis risk in registry-enrolled patients, previously reported in 2021 as 1.02 and 2.09 per 100 pt-y, respectively (Arthritis Rheumatol.2021;73[suppl 9]).

Methods: A web-based data capturing system is used to store patient demographics, history, and medications. The inclusion criteria are positive aPL according to the Updated Sapporo Classification Criteria, tested within one year prior to enrollment. Follow-up occurs every 12±3m with clinical data and blood collection. In this prospective analysis, based on patients who completed 1- to 10-year follow-up visits, we report the incident thrombosis risk in persistently aPL-positive patients with and without a history of thrombosis. Secondarily, we compare baseline clinical and laboratory characteristics of patients with vs without new thrombosis.

Results: As of April 2023, 1,166 patients were enrolled; 22 patients with a prior history of transient ischemic attack and no prior imaging-confirmed thrombosis were excluded. Five other patients were excluded due to incomplete data. Of the remaining 1,139 patients; a) 606 had aPL/APS without SAID, including aPL without APS classification (n=125), thrombotic APS (TAPS, n=357), obstetric APS (OAPS, n=57), and TAPS+OAPS (n=67); and b) 533 patients had aPL/APS associated with SAID, including aPL without APS (n=164), TAPS (n=269), OAPS (n=35), and TAPS+OAPS (n=65). Mean follow-up (enrollment to first new thrombosis or most recent follow-up) was 3.67 years (1401 pt-y) and 4.03 years (3053 pt-y) for those without and with a history of thrombosis, respectively. Based on 14 first events in 14 patients, and 88 recurrent events in 65 patients (Table 1), the incident thrombosis risk was 1.00 and 2.13 per 100 pt-y in patients without and with a history of thrombosis, respectively. Baseline characteristics were similar between aPL-positive patients with (n=14) or without (n=368) first thrombosis, and between APS patients with (n=65) or without (n=692) recurrent thrombosis, except: a) obesity, renal failure, and direct oral anticoagulant use were more common in APS patients with recurrent thrombosis than in those without (p=0.02, 0.01, and 0.005, respectively); and b) smoking history was more common in patients with first thrombosis than in those without (p=0.05) (Table 2). Table 3 describes patient characteristics at the time of new events.

Conclusion: Based on 4,454 pt-y of follow-up, the incident thrombosis risk in persistently aPL-positive patients remains relatively low. Secondary analysis revealed possible differences in medications and cardiovascular risk factors at enrollment between patients with and without thrombosis during follow-up, but these results should be interpreted with caution given the large number of covariates analyzed (multiplicity). Future Cox proportional hazards analysis will help better define the risk and protective factors for thrombosis in persistently aPL-positive patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/first-and-recurrent-thrombosis-risk-after-4454-patient-years-of-follow-up-prospective-results-from-the-antiphospholipid-syndrome-alliance-for-clinical-trials-and-international-networking-aps-action/