Do Patients with Antiphospholipid Syndrome Present with More Significant Venous Thromboembolic Clot Burden? A Retrospective Single-Center Study

<b>Background/Objectives</b>: Venous thromboembolic disease (VTE) is the most common initial manifestation of antiphospholipid syndrome (APS). Determining which patients with VTE to test for APS can be a challenging clinical decision. We aimed to determine if patients with APS present with more significant venous thromboembolic clot burden, as compared to patients with VTE without a diagnosis of APS. <b>Methods</b>: A multi-hospital single-institution retrospective cohort study was designed. Patients with a diagnosis of VTE who had been tested for APS from 1 December 2019 to 31 January 2022 were included. Patients were stratified based on the presence of APS (APS versus non-APS). Significant venous thromboembolic clot burden was defined as PE involving the main and/or lobar pulmonary arteries or DVT involving the iliofemoral veins. Assessment of clot burden was performed by review of radiology reports of the index clotting event. <b>Results</b>: We included 748 patients with a history of VTE who had been tested for APS; 75 patients (10%) were positive for APS. Significant clot burden was present in 29 (38.7%) APS patients and 269 (40.0%) non-APS patients (OR 0.95, 95% CI 0.58-1.56; <i>p</i> = 0.85). No predictors for significant clot burden were found on multivariable analysis. Triple-positive APS (OR 0.83, 95% CI 0.16-4.21; <i>p</i> = 0.82) and primary APS (OR 0.72, 95% CI 0.15-3.45; <i>p</i> = 0.68) were not associated with more significant clot burden. <b>Conclusions</b>: This retrospective single-institution analysis suggests that patients with APS may not present with more significant venous thromboembolic clot burden than patients with VTE without APS.