From the Guidelines
Troponin I and Troponin T are both recommended for diagnosing acute myocardial infarction (MI), with the choice between them depending on laboratory availability rather than clinical superiority. According to the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1, measuring cardiac-specific troponin (either Troponin I or T) at presentation and 3–6 hours after symptom onset is crucial for identifying the pattern of values in patients with suspected acute coronary syndromes (ACS).
The key differences between Troponin I and Troponin T lie in their specificity, with Troponin I being exclusively expressed in cardiac muscle, making it highly cardiac-specific 1. In contrast, Troponin T has minimal expression in skeletal muscle, which can potentially cause false positives in conditions like renal failure or skeletal muscle injury. However, both markers have comparable sensitivity and specificity for acute MI detection, achieving >90% accuracy when using high-sensitivity assays.
When interpreting results, it's essential to note that troponin elevation indicates myocardial injury but doesn't specify the cause, which could include non-ACS conditions like myocarditis, pulmonary embolism, or heart failure 1. The guideline recommends obtaining additional troponin levels beyond 6 hours in patients with initial normal serial troponins and electrocardiographic changes and/or intermediate/high-risk clinical features.
Some key points to consider when using troponin assays include:
- The 99th percentile of the upper reference level as the appropriate cutpoint for considering myocardial necrosis
- Determining not only the peak troponin value but also serial changes
- Clinical laboratory reports should indicate whether significant changes in cardiac troponin values for the particular assay have occurred
- Point-of-care troponin values may provide initial diagnostic information, although their sensitivity is substantially below that of central laboratory methods 1.
Overall, the choice between Troponin I and Troponin T should be based on laboratory availability and the specific clinical context, rather than a perceived clinical superiority of one over the other.
From the Research
Comparison of Troponin I and Troponin T
- The study 2 compared the clinical performance of troponin T and troponin I in diagnosing acute myocardial infarction, finding that troponin T had a sensitivity of 85% and specificity of 87.2%, while troponin I had a sensitivity of 76% and specificity of 76.2%.
- The same study found that when both tests were performed, the sensitivity of troponin T was 100% and specificity was 78%, while the sensitivity of troponin I was 86% and specificity was 78%.
- Another study 3 discussed the use of cardiac troponins I and T as molecular markers for early diagnosis, prognosis, and accurate triaging of patients with acute myocardial infarction, highlighting their good sensitivity and specificity as indicators of myocardial necrosis.
Diagnostic Thresholds and Kinetics
- A study 4 investigated the use of high-sensitivity cardiac troponin I concentrations to differentiate myocardial injury and infarction, finding that troponin concentrations at presentation were insufficient to distinguish type 1 myocardial infarction from other causes of myocardial injury or infarction.
- The study 4 also found that the absolute, relative, and rate of change in troponin concentration were highest in patients with type 1 myocardial infarction, and that combining troponin concentration and change in troponin improved discrimination.
- Another study 2 found that the biggest clinical sensitivity and specificity were achieved when threshold myocardial infarction diagnostic concentration of troponin T was considered >0.04 ng/ml and of troponin I >0.69 ng/ml.
Clinical Interpretation and Performance
- A review 5 discussed the interpretation and performance of diagnostic markers of myocardial injury, including troponin T and I, highlighting their sensitivity and specificity as indicators of myocardial injury.
- The review 5 also noted that elevated troponins can occur in clinical situations other than acute myocardial infarction, such as pulmonary embolism, sepsis, myocarditis, and acute stroke.
- A study 6 found that peak cardiac troponin-T level correlated with scintigraphically determined infarct size and was associated with 12-month mortality in patients undergoing primary percutaneous coronary intervention for acute myocardial infarction.