An evaluation of the cardiac troponin 1 method using Dade Behring's Dimension RxL: sample types and stability

The purpose of this study was to determine if the cardiac troponin I (cTnI) assay utilising Dade Behring's Dimension RxL was sensitive to heparin or ethylenediaminetetraacetic acid (EDTA) interference, and to ascertain if these additives influence cTnI recovery after storage at 2 - 8 C and -20 C. Seventy-three triplicate samples were analysed to compare cTnI values to those obtained in serum. Forty-five additional samples were used to examine sample stability. Serum, heparin plasma and EDTA plasma samples all show similar levels of imprecision at comparable cTnI concentrations. Heparin plasma samples were on average 0.017 g/L higher than the corresponding serum values. EDTA plasma samples were on average 0.185 g/L lower than the corresponding serum values. Across the grey area range of 0.10 - 1.50 g/L cTnI, heparin values were 0.021 g/L higher than serum, and EDTA values were 0.078 g/L higher. After storage at 2 - 8 C, heparin plasma samples showed a significant decrease in cTnI concentration after 24 h, likewise serum samples after 48 h, and EDTA plasma samples after 10 days. Heparin samples are unsuitable for freezing at -20 C, but serum and EDTA plasma samples may be frozen for up to 14 days. The three sample types studied, serum, heparin plasma and EDTA plasma all appear to be of use for the measurement of cTnI concentrations using Dade Behring's Dimension RxL method. Serum would be the preferred sample type for all but anticoagulated patients, with EDTA plasma collections being useful as a guide only for samples greater than 48 h old. Heparin plasma samples are preferred for anticoagulated patients, but can not be used for analysis after 24 h from the initial collection.