Characteristics of cardiac troponin measurements.

Cardiac troponin I (cTnI) and T (cTnT) have displaced myoglobin and creatine kinase-MB as the preferred markers of myocardial injury and have become the cornerstones for diagnosis of myocardial infarction (MI). Current guidelines for MI diagnosis give specific recommendations for cTnI and cTnT assays including instructions to reliably measure values in the range of the 99th percentile of a normal reference cohort with good precision, for example, 10% total coefficient of variation. Unfortunately, the nomenclature system that has evolved for cTnI and cTnT is haphazard and unsystematic. It is key to recognize that not all cTnI and cTnT measurement methods are equivalent; hence, knowledge of local measurements is essential for effective evaluation of patients presenting with suspected non-ST elevation MI. For cTnI, the amino acid sequences frequently targeted for effective measurement include residues 41-49 and 83-93 because these regions of the molecule are stable, helping make the assays reproducible. Use of the recommended cutoff at the 99th percentile of a normal cohort is related to improved patient outcomes. Therefore, use of a troponin assay with good measurement characteristics at the 99th percentile, often referred to as 'sensitive assays', is important for patient outcomes. cTnI and cTnT assays with higher sensitivity are becoming available, and their utilization for measurement in asymptomatic populations may be useful for risk assessment and management in the future. However there is currently no evidence that these high-sensitivity assays confer an advantage in the context of MI diagnosis. Currently cTnI assays are not standardized; thus, there can be a substantial difference in values depending on the assay used. An international effort toward standardization is ongoing, but is not anticipated to be completed and implemented for a few years. Our purpose here is to add insight to important characteristics of troponin measurement techniques and how these features may impact clinical utilization of these tests.