Circulating levels of tissue factor and the risk of thrombosis associated with antiphospholipid syndrome.

The mechanisms behind the severe hypercoagulable state in antiphospholipid syndrome (APS) have not yet been fully elucidated. Knowledge on the etiology of thrombosis in APS is needed to improve treatment. We performed a case control study to evaluate the association of the levels of circulating tissue factor (TF) with thrombotic APS and unprovoked venous thromboembolism (VTE), as compared with controls without a history of thrombosis. Study participants were selected in the same geographic area. Linear regression was used to evaluate possible determinants of TF levels among controls and logistic regression was used to evaluate the association between TF, unprovoked VTE and t-APS. TF levels were grouped into three categories based on: below 50th percentile [reference], between 50-75th percentiles [second category] and 75th percentile [third category]. Two hundred and eighty participants were included in the study; 51 patients with unprovoked VTE, 111 patients with t-APS and 118 control individuals. The levels of TF were not associated with an increased risk of unprovoked VTE, as compared with controls. The adjusted odds ratio for t-APS was 2.62 (95%CI 1.03 to 6.62) with TF levels between 50-75th percentiles and 8.62 (95%CI 3.76 to 19.80) with TF levels above the 75th percentile, as compared with the reference category (below the 50th percentile). In the subgroup analysis, higher levels of TF were associated with both arterial and venous thrombosis in APS and with both primary and secondary APS. Circulating TF is associated with thrombotic complications related to APS, but not with the risk of unprovoked VTE.