Determination of α2-antiplasmin-plasmin complex in human plasma with an enzyme-linked immunosorbent assay

A novel enzyme-linked immunosorbent assay (ELISA) for quantification of α2-antiplasmin-plasmin complex (APP) in undiluted plasma was developed. The assay follows the sandwich principle and uses two different antibodies directed against plasmin-modified α2-antiplasmin and plasminogen, respectively. The antibodies bind selectively to the corresponding antigen moieties of APP. The assay was calibrated with definite concentrations of preformed purified APP added to APP-poor plasma. The lower limit of sensitivity of the assay was 10ng/ml. Mean coefficients of variation of 5.8% (intraassay) and 7.2% (interassay) were found for APP concentrations between 50 and 5000 ng/ml. A reference range from 80–470 ng/ml was calculated from APP concentration in plasma samples from 178 healthy donors (mean value±SD: 210±88). In plasma samples from patients during thrombolytic therapy, APP was found up to 20000 ng/ml. From our data we conclude that quantification of APP can be a sensitive tool for specific detection of an activation of the fibrinolytic system.