Measurement of Different Forms of Tissue Plasminogen Activator in Plasma

Background: We evaluated assays to measure both total tissue plasminogen activator (tPA) and the three princi-ple forms of tPA in plasma: active tPA, tPA complexed with plasminogen activator inhibitor type 1 (PAI-1), and tPA complexed with C1-inhibitor. Methods: Active tPA was measured by use of an indi-rect amidolytic assay and immunofunctional assays. tPA/PAI-1, tPA/C1-inhibitor, and total tPA antigen were measured by use of microtiter plates coated with anti-tPA antibodies and, respectively, anti-PAI-1, anti-C1-in-hibitor, and anti-tPA antibodies conjugated to peroxidase. Results: The immunofunctional tPA assay detected 1 U/L (0.001 U/mL) tPA and recovered 108 % 6 12 % of active tPA added to samples containing high (mean, 60 000 IU/L) PAI-1 activities vs a detection limit of 1