A novel enzyme immunoassay for plasma thrombospondin: Comparison with beta-thromboglobulin as platelet activation marker in vitro and in vivo

A novel enzyme immunoassay for plasma thrombospondin (TSP) based on commerc ially available monoclonal antibodies was established. The following condit ions for correct collection and preservation of blood samples were required : venipuncture directly into a vacutainer containing citrate, theophylline, adenosine and dipyridamole, storage on ice, and separation of plasma withi n 30 minutes. Thereafter, the plasma TSP concentration remained constant at room temperature and after five times of freezing and thawing. Both inter- and intraassay variation coefficients were 5%. The lower detection limit w as 20 mu g/L. Median TSP concentration among 40 healthy blood donors was 43 mu g/L, slightly lower than previously published. The assay is valid, reli able, and has certain advantages compared with previously published methods . TSP and beta-thromboglobulin (BTG) were then compared as platelet activat ion and biocompatibility markers in vivo: 23 patients undergoing cardiopulm onary bypass (CPB); and in vitro: effect of coating polyvinyl chloride with heparin. The kinetic patterns of TSP and BTG were markedly different in vi vo but virtually identical in vitro, explained by different in vivo clearan ce mechanisms during CPB. We conclude that BTG is superior to TSP for evalu ation of platelet activation during in vivo CPB, whereas TSP and BTG are vi rtually identical as markers in vitro. (C) 2000 Elsevier Science Ltd. Al ri ghts reserved.