ACQUIRED ACTIVATED PROTEIN-C RESISTANCE IN PATIENTS WITH LUPUS ANTICOAGULANT AND ESSENTIAL THROMBOCYTHEMIA

The prevalence of activated protein C (APC) resistance and the antigen levels of factor V were assessed in 37 patients with lupus anticoagul ant (LA), 12 with essential thrombocythemia (ET), 17 with idiopathic t hrombocytopenic purpura (ITP), and in 27 cases of thrombotic complicat ions associated with diabetes mellitus and collagen vascular disease. Blood samples taken from 30 healthy normal subjects were also availabl e for comparison. The mean APC ratio of patients with LA (2.9 +/- 1.5) , ET (2.7 +/- 1.2), and secondary thrombosis (2.6 +/- 0.9) were signif icantly lower than that of the healthy control group (3.5 +/- 1.0). Th e APC ratio of ET patients with thrombosis (2.3 +/- 0.6) was significa ntly lower than that measured in ET cases without thrombotic complicat ion (3.9 +/- 1.9). Patients positive for LA and with thrombotic compli cation (1.8 +/- 1.4) presented lower APC ratios than those without thr ombosis (3.3 +/- 1.4). Among all patients, an APC ratio lower than 2 w as found in 24 cases, of which 16 had thrombotic disease, but none of them presented the factor V:R506Q mutation. The antigen levers of fact or V correlated significantly with APC ratio in all patients. The resu lts of this investigation suggest that an acquired poor anticoagulant response to APC might explain, at least in part, the thrombophilia of patients with LA and ET and that associated with diabetes mellitus or collagen disease.