Elevated Microparticle Tissue Factor Activity Differentiates Patients With Venous Thromboembolism in Anti-neutrophil Cytoplasmic Autoantibody Vasculitis.

INTRODUCTION: Venous thromboembolism (VTE) is a life-threatening complication of anti-neutrophil cytoplasmic autoantibody (ANCA) vasculitis whose mechanism remains incompletely elucidated. We tested the hypothesis that elevated microparticle tissue factor activity (MPTFa) or anti-plasminogen antibodies (anti-Plg) may identify patients at risk for VTE. METHODS: In this prospective study, patients were enrolled during active disease and followed longitudinally. Twelve patients who experienced a VTE (VTE(pos)) were compared with patients without VTE (VTE(neg), n = 29) and healthy controls (HC, n = 70). MPTFa, anti-Plg, interleukin-6, high-sensitivity C-reactive protein (hs-CRP), D-dimer, serum creatinine, and serum albumin were assessed. Fisher's exact tests and Wilcoxon tests compared categorical and continuous variables, respectively. Cox regression for time to VTE or last follow-up was performed. RESULTS: VTE(pos) patients had higher MPTFa (peak median = 14.0, interquartile range = 4.3-36.6) than HC (0, 0-3.5) and VTE(neg) patients (0, 0-1.4). In time-to-event analysis, MPTFa was associated with VTE when measured during both active disease (hazard ratio [HR]; 95% confidence interval [CI]: 1.04; 1.01-1.08) and remission (1.4; 1.11-1.77). Anti-Plg during remission was also associated with VTE (1.17; 1.03-1.33). Each g/dl decrease of serum albumin was associated with a 4-fold increase in VTE risk (4.4; 1.5-12.9). Adjusting for estimated glomerular filtration rate (eGFR), anti-Plg during remission remained significantly associated with VTE. CONCLUSION: Elevated MPTFa and increased anti-Plg in remission are strong indicators of VTE independent of renal function. Association of anti-Plg during remission with VTE implies hypercoagulability even during disease quiescence. Hypoalbuminemia strongly portends VTE risk, which is a novel finding in ANCA vasculitis. A thrombotic signature would allow improved management of patients to minimize VTE risk and complications of anticoagulation.