Increased activated protein C-protein C inhibitor complex level in patients positive for lupus anticoagulant

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Abstract
Activated protein C (APC)-protein C inhibitor (PCI) complex and APC-α1antitrypsin (α1AT) complex levels were measured in 29 patients positive for lupus anticoagulant (LA). LA was considered positive if two of the following three criteria were fulfilled: (1) prolongation of the activated partial thromboplastin time, (2) prolongation of the kaolin clotting time (KCT) and KCT mixing test, and (3) prolongation of the dilute Russell's viper venom time (DRWT) and DRWT/DR WT with high lipid concentration. Plasma thrombin-antithrombin III (AT-III) complex and plasmin-α2-antiplasmin inhibitor complex levels in patients positive for LA were increased slightly, but not significantly, and FDP-d-dimer and t-PA levels were not markedly increased. Plasma PAI-1 level in the LA-positive patients was significantly increased compared with normal volunteers. AT-III activity, protein C antigen, PCI antigen, and protein S antigen levels in the LA-positive patients were virtually normal, while protein C activity was slightly, but not significantly, decreased. APC-PCI complex level was increased in all LA-positive patients, and was not detectable in patients with systemic lupus erythematosus and normal volunteers. APC-α1AT complex was increased slightly, in only two LA-positive patients; it was not detectable in the other patients or in the normal volunteers. These findings suggest that patients positive for LA are in a hypercoagulable state and that protein C activity in such patients is decreased, due to the activation of this protein.

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