The antithrombin III content of cryoprecipitate prepared from blood collected with and without heparin.

Antithrombin III (AT III) is a plasma protein which acts as the principal inhibitor of thrombin and is a major modulator of intravascular coagulation. Hereditary deficiency of AT III leads to recurrent episodes of thromboembolism. Acquired deficiency of AT III occurs in persons with a variety of conditions, including severe liver disease and disseminated intravascular coagulation. Replacement of AT III may be important in some deficient persons. To determine if cryoprecipitate is a useful source of AT III, we measured the AT III content of cryoprecipitate prepared from citrate phosphate dextrose blood using coagulation and fluorogenic assays and immunoassays. Using the fluorogenic assay, we also determined the effect of adding heparin to blood on the cryoprecipitation of AT III. Functional and antigenic AT III levels were similar to those of normal plasma in all citrate phosphate dextrose blood units tested, indicating that AT III is not concentrated in cryoprecipitate. Heparin had no effect on the cryoprecipitation of AT III.