Troponin T and I assays show decreased concentrations in heparin plasma compared with serum: Lower recoveries in early than in late phases of myocardial injury

Background: Heparinized plasma samples allow more rapid analysis than serum samples, but preliminary studies showed lower cardiac troponin T (cTnT) re sults in plasma. We undertook a multicenter study to characterize this effe ct for cTnT and cardiac troponin I (cTnI). Methods: Blood samples were collected with and without heparin at five hosp itals, cTnT was measured by a "third generation" assay (Elecsys(R)), and cT nI was measured by a commercial immunoassay (IMMULITE(R)). Results: Mean cTnT was 15% lower in heparin sampling tubes than in serum. M easured concentrations of cardiac troponins also decreased with increasing heparin concentrations added to sera. Heparin-induced losses were greater i n early than in late phases after onset of chest pain. Addition of heparin (similar to 100 IU/mL) to serial samples from nine acute myocardial infarct ion patients produced mean cTnT losses of 33% at 1-12 h after onset of ches t pain, 17% at 13-48 h, and 7% after 48 h. The changing heparin effects wer e seen for both cTnT and cTnI during time courses of individual patients wi th myocardial infarction. Conclusion: We suggest that binding of heparin to troponins decreases immun oreactivity, especially in early phases of myocardial injury. The resulting losses may depend on the antibodies used in each troponin assay. (C) 2000 American Association for Clinical Chemistry.