Clinical meaning
Cardiac troponins (cTnI and cTnT) are structural proteins of the cardiomyocyte sarcomere that regulate calcium-mediated actin-myosin interaction during cardiac muscle contraction. The troponin complex consists of three subunits: troponin C (calcium-binding), troponin I (inhibitory — prevents actin-myosin interaction in the absence of calcium), and troponin T (tropomyosin-binding — attaches the complex to the thin filament). Troponin I and T exist in cardiac-specific isoforms (cTnI and cTnT) that are not expressed in skeletal muscle, making them highly specific biomarkers for myocardial injury. When cardiomyocytes are damaged — whether from ischemia, inflammation, toxins, or mechanical stress — the sarcomeric structure is disrupted and troponin proteins are released into the bloodstream. High-sensitivity troponin (hs-cTn) assays can detect circulating troponin at concentrations 10-100 times lower than conventional assays, enabling earlier detection of myocardial injury (as early as 1-3 hours after symptom onset vs 6-12 hours for conventional assays). The 99th percentile upper reference limit (URL) is the diagnostic cutoff for myocardial injury. Troponin elevation with a dynamic rise-and-fall pattern (delta change of 20% or more at 3 hours) distinguishes acute myocardial injury (including MI)...