BACKGROUND Tissue factor pathway inhibitor (TFPI) is an anticoagulant which modulates the tissue factor (TF) dependent pathway, acting on the factor VIIa/TF complex, factor Xa, and thrombin. Although most TFPI is found in association with plasma lipoproteins and platelets, the functional pool is bound to vascular endothelium and is released into the circulation on stimulation with heparin or low molecular weight heparin (LMWH).

OBJECTIVE To assess the vascular endothelial TFPI pool in patients with Behçet's disease (BD) or systemic lupus erythematosus (SLE).

RESULTS Baseline median TFPI was 149.5 ng/ml in healthy subjects, and the percentage change in TFPI at 20 minutes (((value at 20th min − baseline value)/baseline value) × 100) was 575.2. TFPI concentrations in patients with BD were initially normal at baseline (136.0 ng/ml), but the percentage change (44.7) was significantly lower than in the patients with SLE and the controls. Baseline TFPI concentrations in patients with SLE (83.0 ng/ml) were lower than in the control group, but the TFPI response to stimulation with LMWH reached a level (626.4%) comparable to that of the controls.

CONCLUSION Depletion of the functional endothelial pool in BD and low circulating concentrations of TFPI despite an intact pool in SLE may be important in the pathogenesis of thrombosis in these vasculitic syndromes.