Are troponin I and T interchangeable biomarkers?

The most recent international guidelines recommend that high-sensitivity (hs) methods should be preferred for the measurement of cardiac troponin I (cTnI) and T (cTnT) for the detection of myocardial injury and the differential diagnosis of acute coronary syndromes. Furthermore, these guidelines state that there is no significant difference in accuracy among hs cTnI and cTnT methods for diagnosis of acute myocardial infarction. Myocardial injury is a prerequisite for the diagnosis of acute myocardial infarction, but it is also a distinct entity. The 2018 Fourth Universal Definition of Myocardial Infarction states that myocardial injury is detected when at least one value above the 99th percentile upper reference limit is measured in a patient by high-sensitivity methods for cTnI or cTnT. Occasionally, discrepancies between hs-cTnI and hs-cTnT test results can be found, when tested in the same blood sample. Several studies have reported discrepancies between hs-cTnI and hs-cTnT test results in some clinical conditions (especially chronic neuromuscular diseases) or even in apparently healthy subjects. This review, summarizes and discusses the biochemical, pathophysiological and analytical possible mechanisms causing discrepancies between hs-cTnI and hs-cTnT test results.