Objective: Tissue factor (TF) is the major intrinsic initiator of clotting. TF expression on monocytes has been associated with high titers of anticardiolipin antibodies (aCL) in patients with antiphospholipid syndrome (APS) with thrombosis. We investigated the influence of clinical factors on TF activity in blood from patients with systemic lupus erythematosus (SLE) and examined the relationship between aCL and TF.
Methods: In this cross sectional study, consecutive patients with SLE from one rheumatology clinic gave blood samples for measurement of TF activity, aCL, and Russell viper venom time. We assessed disease activity by measuring sedimentation rate, anti-dsDNA, and complement components C3 and C4, and measured clinical indices. Associations were investigated with the Wilcoxon rank-sum test and linear regression.
Results: Sixty-nine patients contributed blood samples. The median age was 38 years, and 10 of the SLE patients had a history of thrombosis. Patients with active arthritis had TF activity 1.3 times that in patients without arthritis (p = 0.028). Users of nonsteroidal antiinflammatory drugs (NSAID) had TF activity significantly lower than nonusers (p = 0.010). Patients with previous thrombosis had TF activity significantly lower than patients without thrombosis (p < 0.001). Overall, aCL and TF activity were not associated when we adjusted for these clinical factors.
Conclusion: Arthritis, previous thrombosis, and use of NSAID significantly modified TF activity in patients with SLE. Unlike previous reports, we found no association between aCL titer and TF activity, which may be due to our adjusting for other important clinical factors.