Protein C activity in patients with antiphospholipid syndrome.

The interaction between antiphospholipid antibodies and the protein C system may explain at least a part of the mechanisms underlying thrombosis in the antiphospholipid syndrome (APS). We evaluated the protein C activity, factor V Leiden mutation and the presence of several types of antiphospholipid antibodies in 60 patients with antiphospholipid syndrome. Nineteen patients (31.