Determination of main inhibitor of activated factor XI.

To study the contribution of alpha 1 antitrypsin (alpha 1AT) and antithrombin III (AT III) to the inactivation of F.XIa in plasma, we developed the assay system of F.XIa-AT III complex according to our method of F.XIa-alpha 1AT complex, and measured the levels of both complexes in the patients with disseminated intravascular coagulation (DIC) derived from various triggers. F.XIa-alpha 1AT complex level was always higher than F.XIa-AT III complex level in each patient, independently on the trigger of DIC, the administration of heparin and the levels of F.XI, alpha 1AT and AT III. These results indicate that alpha 1AT is the main inhibitor of F.XIa in plasma.