Lower Cardiac Troponin T and I Results in Heparin-Plasma Than in Serum

Abstract

Background: The use of plasma rather than serum for determination of cardiac troponins can improve turnaround time and potentially avoid incomplete serum separation that may produce falsely increased results. We investigated the influence of incomplete serum separation and the effect of heparin-plasma on cardiac troponin concentrations. Methods: Serum and heparin-plasma samples were drawn simultaneously from 100 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). Serum samples were reanalyzed after a second centrifugation to assess the influence of incomplete serum separation. Results: Mean results (± 95% confidence interval) in heparin-plasma compared with serum were 101% ± 2% (AxSYM cTnI), 94% ± 3% (ACS:Centaur cTnI), and 99% ± 3% (Elecsys cTnT). Differences >20% were seen in 11% of results 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 between serum and plasma was independent of the absolute concentration and confined 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.

Cardiac Troponins in Dogs and Cats

“…Serum and plasma values are significantly correlated, but a tendency toward slightly lower serum concentrations has been documented in dogs, 54 whereas the opposite has been found in humans. 54,64 Separate reference intervals might, therefore, be needed. Troponin reportedly has long-term stability at À70 to À80°C, 8,65 but is not stable at room temperature, 54 refrigerator temperature, 60 or À20°C.…”

Serum and plasma cardiac troponin I concentrations in clinically normal Thoroughbreds in training in Australia

“…The findings from one cTnI assay therefore cannot be extrapolated to another unless the assays have been calibrated and have comparable analytical performance at the same clinical decision levels 1 . A difference has also been reported 7,8 between serum and heparinised plasma in human clinical samples. The purpose of this paper is to report the findings of measurements of cTnI in normal horses from both serum and heparinised plasma analysed through a standard Australian commercial laboratory (Mayne Health Vetnostics).…”

Agreement between troponin T levels from plain and heparinized tubes

“…Two recently published studies showed a decrease in cTnT levels measured in plasma compared with serum samples 1,2 . One showed an average difference of 15% 1 and the other showed no difference on average, but an idiosyncratic relative difference of > 20% between samples in eight of 100 cases 2 . Both groups of authors concluded that cTnT samples should not be collected in heparinized tubes.…”

“…Hence, none of these results would have been considered as negative if one took 0.03 µg/L as the upper reference limit cut‐off for the test, given that the reproducibility of the test is 0.03 µg/L and no cTnT should normally be detected in the blood. Similarly, Stiegler et al 2 only included values > 0.05 µg/L in both tubes. All eight samples that showed a relative difference of > 20% in this study had concentrations of cTnT higher than 0.2 µg/L in both tubes and would have been treated as a positive result by a clinician managing the patient, regardless of the collection method.…”

“…The quantitative measurement of cardiac troponins T and I (cTnT and cTnI, respectively) is now a routine step in the evaluation of chest pain in the emergency department (ED). Concern has been raised that collection of blood in heparinized (plasma) tubes may lead to false low measurements of cTnT and cTnI when compared with a non‐heparinized serum sample 1,2 . The effect is thought to be idiosyncratic resulting in up to a 15% difference between serum and plasma tubes 1 .…”