Plasma or serum samples: measurements of cardiac troponin T and of other analytes compared

Abstract

Conflicting data in the literature concern possible differences in the immunochemical measurement of cardiac troponins, either in plasma or in serum. In order to address this specific point, 96 serum and heparin-plasma pairs were obtained for cardiac marker measurement [cardiac troponin T (cTnT); myoglobin (Myo) and creatine kinase-MB isoenzyme (CK-MB)]; 29 additional "common" analytes were measured in 77 such samples. The cardiac markers were measured by electrochemiluminescence (Elecsys 2010, Roche); the other analytes by established automated methods (Modular, Roche). Mean plasma/serum ratios for cTnT (0.95), creatine kinase-MB (1.01) and myoglobin (0.99) were comparable with those of the 29 common analytes (interval of means 0.83-1.05). The distribution of the plasma-serum differences also showed similarities between cardiac markers and other analytes. A few outlier plasma-serum differences (3-5%) were measured for both categories of analytes. Addition of heparin to serum (51 samples) caused decreased cTnT (mean ratio 0.92). In 3 of 51 such samples the cTnT decrease was more marked, but in a second sample from the same subjects (1 week later) such a prominent, heparin-induced loss of cTnT no longer appeared. In conclusion, plasma-serum differences in immuno-reactive cTnT compare with those observed for other analytes. In occasional heparin-plasma samples immunochemical measurement of cTnT may give exceptionally low values. However, in our sample group of 96 patients (cTnT lower or higher than the cut-off in, respectively, 24 and 72 patients), no misclassification occurred if plasma instead of serum cTnT values were considered.

Increases in plasma corin levels following experimental myocardial infarction reflect the severity of ischemic injury

“…Corin levels were measured in plasma [ 11 , 14 , 15 ] and serum [ 12 , 13 ] in different studies. Comparison of other cardiac markers, such as cardiac troponin T, creatine kinase-muscle/brain and myoglobin showed similar results in both fluids [ 30 , 31 ] which suggests that the sample type (plasma vs. serum) is unlikely to be the key factor associated with different findings among the studies. Protease activity in blood samples might also influence the measured corin levels, but protease inhibition in blood samples was not specified in these studies [ 12 – 14 ].…”

Thrombin-Accelerated Quick Clotting Serum Tubes: An Evaluation with 22 Common Biochemical Analytes

“…Plasma has its own set of areas for concern, for example, problem of adequate mixing of blood with anticoagulants, difference in result values for some analytes when measured in serum or plasma, especially potassium and lactate dehydrogenase, thus requiring changes in reference intervals [5]. With its inherent known limitations particularly in the more recent reports of issues with cardiac markers, plasma may not be the specimen of choice [6–9]. …”

Multiple molecular forms of circulating cardiac troponin: analytical and clinical significance

“…This is of critical importance due to the heavy reliance on diagnostic and prognostic decision-making in the initial hours after onset of chest pain. More recently, in studies for both cTnT 76 and cTnI, 77 similar in vitro concentrations have been reported in serum and plasma; however, in the study by Wang et al 77 citrate anticoagulant rather than heparin was used for cTnI determination. More importantly, in the 96 matched serum plasma samples studied by Dominici et al 76 there were no misclassifications, if plasma was used instead of serum.…”