Acquired Activated Protein C Resistance in Patients with Lupus Anticoagulant and Essential Thrombocythemia

Abstract

The prevalence of activated protein C (APC) resistance and the antigen levels of factor V were assessed in 37 patients with lupus anticoagulant (LA), 12 with essential thrombocythemia (ET), 17 with idiopathic thrombocytopenic purpura (ITP), and in 27 cases of thrombotic complications associated with diabetes mellitus and collagen vascular disease. Blood samples taken from 30 healthy normal subjects were also available 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 significantly lower than that of the healthy control group (3.5 ± 1.0). The APC ratio of ET patients with thrombosis (2.3 ± 0.6) was significantly lower than that measured in ET cases without thrombotic complication (3.9 ± 1.9). Patients positive for LA and with thrombotic complication (1.8 ± 1.4) presented lower APC ratios than those without thrombosis (3.3 ± 1.4). Among all patients, an APC ratio lower than 2 was found in 24 cases, of which 16 had thrombotic disease, but none of them presented the factor V:R506Q mutation. The antigen levels of factor V correlated significantly with APC ratio in all patients. The results 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. Key Words: APC resistance—Lupus anticoagulant—Essential thrombocythemia.