CTn

Cardiac troponin, or cTn, is a protein complex that regulates contraction in heart muscle. It consists of three subunits: troponin C (cTnC), troponin I (cTnI) and troponin T (cTnT). In humans, the cardiac-specific isoforms are cTnI and cTnT, encoded by TNNI3 and TNNT2, while cTnC has both cardiac and skeletal forms. Clinically, measurement of cTnI or cTnT in blood is a sensitive marker of cardiomyocyte injury.

Functionally, the troponin complex sits on the thin filament of the sarcomere. When calcium binds to cTnC, a conformational change relieves inhibition by cTnI, allowing actin-myosin interaction and muscle contraction. cTnT helps anchor the complex to tropomyosin on the filament.

In medicine, cardiac troponins I and T are used primarily as biomarkers for myocardial injury. High-sensitivity assays can detect very low troponin levels and distinguish small changes over time. An elevated cTnI or cTnT, especially with a rising or falling pattern, supports myocardial injury and is central to diagnosing acute myocardial infarction in the appropriate clinical context. However, troponin elevations can occur in various non-ischemic conditions such as myocarditis, heart failure, pulmonary embolism, renal failure, sepsis, and after major surgery or strenuous exercise. Therefore troponin results must be interpreted with symptoms, ECG findings, imaging, and other clinical information.

Timing is important: troponins typically rise within a few hours of injury, peak within about a day, and remain above the normal range for days to weeks, with the exact duration influenced by the assay type and patient factors.