Clinical Information

Cardiac troponin I (cTnI) is a regulatory subunit of the troponin complex associated with the actin thin filament within cardiac muscle cells. Troponin I, in conjunction with troponins C and T, plays an integral role in muscle contraction regulation. Three distinct tissue-specific isoforms of troponin I have been identified from skeletal and cardiac muscles. The cardiac isoform exhibits only 60% similarity with the skeletal muscle isoform and contains additional amino acids at the N-terminus.

High sensitivity troponin assays have been defined as those which can achieve ≤ 10% CV at the 99th percentile of a healthy population and can detect troponin in > 50% of both men and women individually. Clinical studies have demonstrated the release of cTnI in the blood stream within hours following a myocardial infarction (MI) or ischemic injury. High sensitivity assays can detect elevated levels of cTnI (above 99th percentile in an apparently healthy reference population) within 3 hours after onset of chest pain. Cardiac troponin I reaches peak concentration in about 8 to 28 hours and remains elevated for 3 to 10 days following MI. Cardiac troponin is the preferred biomarker for the detection of myocardial infarction based on improved sensitivity and superior tissue-specificity compared to other available biomarkers of necrosis, including CK-MB, myoglobin, lactate dehydrogenase, and others. The high tissue specificity of cTnI measurements is beneficial for identifying myocardial infarction in clinical conditions involving skeletal muscle injury resulting from surgery, trauma, extensive exercise, or muscular disease.

High tissue specificity of cTnI, however, should not be confused with specificity for the mechanism of injury e.g., MI versus myocarditis. When increased cTnI values are encountered (e.g., exceeding the 99th percentile of a reference control population) in the absence of evidence of myocardial ischemia, other etiologies for cardiac damage should be considered. Elevated troponin levels may be indicative of myocardial injury associated with heart failure, renal failure, chronic renal disease, myocarditis, arrhythmias, pulmonary embolism, or other clinical conditions.