On the comparison of serum and plasma samples in troponin assays

Thrombin-accelerated quick clotting serum tubes: an evaluation with 22 common biochemical analytes

Clot activator serum tubes have significantly improved turnaround times for result reporting compared to plain tubes. With increasing workload and service performance expectations confronting clinical laboratories with high-volume testing and with particular emphasis on critical analytes, attention has focussed on preanalytical variables that can be improved. We carried out a field study on the test performance of BD vacutainer rapid serum tubes (RSTs) compared to current institutional issued BD vacutainer serum separator tubes (SSTs) in its test result comparability, clotting time, and stability on serum storage. Data from the study population (n = 160) of patients attending outpatient clinics and healthy subjects showed that results for renal, liver, lipids, cardiac, thyroid, and prostate biochemical markers were comparable between RSTs and SSTs. Clotting times of the RSTs were verified to be quick with a median time of 2.05 min. Analyte stability on serum storage at 4°C showed no statistically significant deterioration except for bicarbonate, electrolytes, and albumin over a period of 4 days. In conclusion, RSTs offered savings in the time required for the clotting process of serum specimens. This should translate to further trimming of the whole process from blood collection to result reporting without too much sacrifice on test accuracy and performance compared to the current widely used SSTs in most clinical laboratories.

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

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.