What is the difference between Troponin I (cardiac troponin I) and Troponin T (cardiac troponin T)?

From the Guidelines

Troponin I and Troponin T are both effective cardiac biomarkers for detecting heart damage, with the choice between them often based on institutional preference and available testing platforms rather than significant clinical differences, as indicated by the 2014 AHA/ACC guideline 1. When considering the diagnosis of myocardial infarction, both Troponin I and Troponin T are valuable, but their characteristics differ slightly.

• Troponin I is highly specific to cardiac muscle with virtually no expression in skeletal muscle, making it highly specific for cardiac injury.
• Troponin T, while also cardiac-specific, has slightly lower specificity due to potential elevations in skeletal muscle diseases and renal failure. The time course for both biomarkers is similar, with elevations detectable a few hours after cardiac damage and remaining elevated for several days.
• Troponin I rises within 4-6 hours, peaks at 12-24 hours, and can remain elevated for 7-10 days.
• Troponin T follows a similar pattern, rising within 3-4 hours, peaking at 10-24 hours, and remaining detectable for up to 14 days. The diagnostic cut-off for myocardial infarction is defined as a cardiac troponin measurement exceeding the 99th percentile of a normal reference population using an assay with an imprecision of ≤10% at the upper reference limit, as supported by the European Society of Cardiology 1 and the American College of Cardiology 1. In clinical practice, the decision to use Troponin I or Troponin T should be based on the availability of assays and institutional protocols, with the understanding that both provide valuable information about cardiac damage when interpreted in the appropriate clinical context, including considerations of serial changes and the clinical presentation of the patient 1.

From the Research

Comparison of Troponin 1 and Troponin 2

• The studies 2, 3, 4, 5, 6 compared the clinical performance of troponin T and troponin I in diagnosing acute myocardial infarction.
• The sensitivity and specificity of troponin T and troponin I tests were investigated in patients with suspected acute coronary syndrome.
• According to the study 2, the sensitivity of troponin T test was 85% and the specificity was 87.2%, while the sensitivity of troponin I test was 76% and the specificity was 76.2%.

Diagnostic Accuracy

• The study 3 found that a sensitive troponin I assay had a higher diagnostic accuracy than a troponin T assay, with an area under the receiver-operating-characteristic curve (AUC) of 0.96 compared to 0.85.
• The sensitive troponin I assay had a clinical sensitivity of 90.7% and a specificity of 90.2% on admission, with a cutoff value of 0.04 ng per milliliter.
• The study 4 compared a high-sensitivity troponin I rapid assay with a high-sensitivity troponin T routine assay and found that the diagnostic value of hs-cTnI was comparable to that of hs-cTnT.

Troponin Thresholds and Kinetics

• The study 6 investigated the use of troponin thresholds and kinetics to differentiate myocardial injury and myocardial infarction.
• The study found that troponin concentrations at presentation were insufficient to distinguish type 1 myocardial infarction from other causes of myocardial injury or infarction in practice.
• The absolute, relative, and rate of change in troponin concentration were highest in patients with type 1 myocardial infarction, and discrimination improved when troponin concentration and change in troponin were combined compared to troponin concentration at presentation alone.

Clinical Performance

• The study 5 discussed the clinical performance of cardiac troponin T and its use in diagnosing myocardial infarction and predicting cardiovascular risk.
• The study found that even minor elevations in troponin levels provided important prognostic information and were associated with adverse outcomes in both acute coronary syndrome and non-acute coronary syndrome conditions.