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) results in plasma. We undertook a multicenter study to characterize this effect for cTnT and cardiac troponin I (cTnI).


METHODS
Blood samples were collected with and without heparin at five hospitals. cTnT was measured by a "third generation" assay (Elecsys((R))), and cTnI was measured by a commercial immunoassay (IMMULITE((R))).


RESULTS
Mean cTnT was 15% lower in heparin sampling tubes than in serum. Measured concentrations of cardiac troponins also decreased with increasing heparin concentrations added to sera. Heparin-induced losses were greater in early than in late phases after onset of chest pain. Addition of heparin ( approximately 100 IU/mL) to serial samples from nine acute myocardial infarction patients produced mean cTnT losses of 33% at 1-12 h after onset of chest pain, 17% at 13-48 h, and 7% after 48 h. The changing heparin effects were seen for both cTnT and cTnI during time courses of individual patients with myocardial infarction.


CONCLUSION
We suggest that binding of heparin to troponins decreases immunoreactivity, especially in early phases of myocardial injury. The resulting losses may depend on the antibodies used in each troponin assay.