Validation of the 99th percentile cutoff independent of assay imprecision (CV) for cardiac troponin monitoring for ruling out myocardial infarction.

By definition, the probability that a single measured cardiac troponin result exceeds the estimated 99th percentile is equal to 0.01 (1%) for a person randomly selected from the general (reference) population. This is irrespective of the imprecision profile of the analytical method as well as the lack of standardization of cardiac troponin assays (1)(2)(3)(4)(5)(6)(7). However, the probability that a measured result exceeds the 99th percentile limit for a specific person from the reference population will vary depending on that person’s true concentration and on the imprecision profile of the specific analytical method. Furthermore, the overall probability that at least one of multiple measured values (the second or third measured cardiac troponin concentration in a timed series of cardiac troponin orders) exceeds the 99th percentile also will vary depending on the imprecision of the analytical method. To investigate the influence of assay imprecision on the likelihood of misclassifying healthy individuals or patients without myocardial injury, we simulated the distribution of cardiac troponin I (cTnI) results in a general population and added random analytical error reflecting different assay imprecision profiles. One imprecision profile assumes a CV of 37.5% at a cTnI of 0.05 μg/L, decreasing to a CV of 25% at a cTnI of 0.07 μg/L, …