Hemostatic System Activation in Patients with Lupus Anticoagulant and Essential Thrombocythemia

Hemostatic system activation was estimated in the plasmas of 39 patients with LAC and 19 patients with ET by measuring concentrations of TAT complex and prothrombin F1+2. The concentrations of FVII, recognized previously as a risk factor for arterial thrombosis, were also measured. None of the patients had active thrombosis during this study. The mean TAT and F1+2 levels in LAC and ET plasmas were higher than the respective values in the plasmas of healthy control subjects. Compared with their respective controls, TAT levels were significantly higher in the LAC group (P < 0.05) and F1+2 was significantly higher in the ET group (P < 0.005). The mean FVIIt and FVIIz was significantly higher (P < 0.05 and P < 0.01, respectively) in LAC than control plasmas. Furthermore, the differences between FVIIt and FVIIz were significantly greater in LAC than control plasmas, indicating increased in vivo proteolysis of FVII in LAC. Although the mean concentrations of these two FVII parameters in ET plasma were not significantly different from those of normal plasmas, the FVII levels were higher in 30% of ET plasmas than the upper limit of controls. Our results are consistent with hypercoagulation in LAC and ET patients, and this may be a contributory factor for the increased rates of thrombosis associated with the two conditions.