Anti-phospholipid antibody syndrome occurrence in patients with persistent anti-phospholipid antibodies.

We investigated the overall frequency of anti-phospholipid syndrome (APS) occurrence in Korean patients with consecutively detected anti-phospholipid antibodies with an interval of 12 weeks (persistent aPLs). We retrospectively reviewed the results of blood tests of aPLs in 14,889 patients in whom aPL tests were performed at Yonsei University College of Medicine, Severance Hospital, from January 2012 to August 2018, and included 833 patients with persistent aPLs. We obtained clinical and laboratory data including anti-cardiolipin antibodies IgM and IgG, anti-beta2 glycoprotein1 IgM and IgG, and lupus anticoagulant (LAC). Of 833 patients with persistent aPLs, 96 patients (11.5%) had APS (84 patients had thrombotic events and 12 had pregnancy morbidity). Among aPLs, LAC was detected in patients with APS more frequently than asymptomatic carriers of aPLs (46.9% vs. 25.9%, p < 0.001). Patients with LAC (relative risk (RR) 2.558, p < 0.001) and aPLs ≥ 2 (RR 1.731, p = 0.014) exhibited the higher rate of APS occurrence than those without. Moreover, patients with aPLs ≥ 3 and aPLs ≥ 4 exhibited the higher rates of APS occurrence than those without (RR 2.753, p < 0.001 and RR 3.209, p = 0.013). Meanwhile, patients with ANA, anti-dsDNA, anti-SSA/Ro, and SLE exhibited the increased frequency of LAC positivity, compared to those without (RR 3.304, p = 0.005, RR 4.269, p = 0.032, RR 3.750, p = 0.041 and RR 8.828, p < 0.001, respectively). APS occurs in 11.5% of Korean patients with persistent aPLs. LAC positivity and aPLs ≥ 2 were significantly associated with APS occurrence. SLE and SLE-related autoantibodies were associated with LAC positivity.