Advances in Cardiac Troponin Composition Assays: A Step Closer to the Clinic?

Cardiac troponin (cTn) is present in cardiomyocytes as a ternary complex of cTnI, cTnT, and troponin C. However, in the event of myocardial injury and release into the extracellular environment, the composition of cTn in the blood is heterogenous. The different circulating cTn forms have been studied over many years using analytical techniques such as gel filtration and western blotting (1). While providing valuable information, these methodologies have limitations. Analysis of different cTn forms using gel filtration, for example, is limited to samples with a high cTn concentration. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) with western blotting can distinguish the different sizes of cTnT, cTnI, and their fragments individually, but as it is a denaturing technique it is not suitable for distinguishing the different forms and sizes of the ternary cTnTIC complex as a whole. In addition, both techniques are not suitable for the clinical laboratory, which generally requires cTn assays to be automated, fast, sensitive, and high-throughput. Over the last decade, the interest in cTn composition has increased significantly, at least in part due to the advent of high-sensitivity cTn immunoassays and the increasing detection of cTn in myocardial injury other than myocardial infarction (MI).