Lower cardiac troponin T and I results in heparin-plasma than in serum

Background: The use of plasma rather than serum for determination of cardia c troponins can improve turn-around time and potentially avoid incomplete s erum separation that may produce falsely increased results. We investigated the influence of incomplete serum separation and the effect of heparin-pla sma on cardiac troponin concentrations. Methods: Serum and heparin-plasma samples were drawn simultaneously from 10 0 patients (50 patients with acute coronary syndrome and 50 patients after open heart surgery) and measured on three different analytical systems, two for determination of cardiac troponin I (cTnI; Abbott AxSYM and Bayer ACS: Centaur) and one for cardiac troponin T (cTnT; Roche Elecsys cTnT STAT). Se rum samples were reanalyzed after a second centrifugation to assess the inf luence of incomplete serum separation. Results: Mean results (+/- 95% confidence interval) in heparin-plasma compa red with serum were 101% +/- 2% (AxSYM cTnI), 94% +/- 3% (ACS:Centaur cTnI) , and 99% +/- 3% (Elecsys cTnT). Differences >20% were seen in 11% of resul ts on the ACS:Centaur, 9% of results on Elecsys cTnT, and 2% of results on the AxSYM. For the Elecsys cTnT assay, the magnitude of the difference betw een serum and plasma was independent of the absolute concentration and conf ined to individual samples, and was reversed by treatment with heparinase. A second centrifugation had no effect on serum results by any of the assays . Conclusion: The concentrations of troponins measured in heparin-plasma are markedly lower than in serum in some cases. (C) 2000 American Association f or Clinical Chemistry.