To investigate plasma levels of natural anticoagulant proteins such as protein S, protein C and antithrombin III in a selected population of patients with rheumatoid arthritis (RA) with and without anticardiolipin antibody (aCL) positivity, and to evaluate the possible relationships with an increased risk of thrombotic events in RA.
A total of 184 female RA patients attending our Extra-Articular Involvement RA Clinic were evaluated for aCL levels, total and free protein S, protein C and antithrombin III concentrations, and for the occurrence of thrombotic events. Patients were grouped as aCL positive (n = 35) and aCL negative (n = 149).
Higher rates of venous and/or arterial thromboses were diagnosed in patients with RA compared to controls (P = 0.01). In particular, lower free protein S levels were found in aCL-positive patients with RA compared to both aCL-negative patients and controls (P = 0.001). Functional assays for protein C, antithrombin III as well as total protein S levels were found to be in the normal range in all patients and controls.
The association observed between aCL positivity and decreased levels of free protein S in RA patients may represent one of the risk factors for thrombotic events.