Statistical Analysis
Continuous variables are presented as means
(±SD) or medians (with the interquartile range),
and categorical variables as numbers and percentages.
Continuous variables were compared with
the use of the Mann–Whitney U test and categorical
variables with the use of the Pearson chi-square
test. Receiver-operating-characteristic (ROC) curves
were constructed to assess the sensitivity and
specificity of cardiac troponin measurements obtained
at specific times with the five assays and
to compare their ability to diagnose acute myocardial
infarction. Logistic regression was used
to combine cardiac troponin levels at presentation
with early changes in cardiac troponin levels.
The comparison of areas under the ROC curves
(AUC) was performed as recommended by DeLong
et al.22 All hypothesis testing was two-tailed, and
P values of less than 0.05 were considered to indicate
statistical significance. All statistical analyses
were performed with the use of SPSS for Windows,
version 15.0 (SPSS), and MedCalc software,
version 9.6.4.0 (MedCalc).