Are all troponin assays equivalent in the emergency department?

Cardiac-specific troponins (cTn) are recently-introduced, sensitive and specific markers of myocardial injury, and their absence should allow to safely exclude a coronary event. Various assays are commercially available but the relative advantage of each is not clear. Our objective was to compare the reliability of the two most commonly used troponin assays (cTnI and cTnT), in the emergency department (ED) for clinical decision when myocardial infarction (MI) or acute coronary syndrome (ACS) is suspected.

This prospective study included all patients arriving at the ED over a six-month period with chest pain or symptoms suggesting MI or ACS, in which diagnosis could not be confirmed due to absence of characteristic ECG features. All patients were tested with at least one of the two troponin assays available at the ED.

Of the 54 included patients, ten (19%) were eventually diagnosed with MI/ACS. Qualitative assays for cTnI and cTnT identified the MI/ACS patients by both assays (respective positive predictive values of 0.5 and 0.7, and negative predictive values of 1.0 and 0.9). However, these assays were only partially correlated (R equals 0.49) and differed significantly. The quantitative assay for cTnI, but not for cTnT, discerned those who had MI/ACS (group A) from those who had other condition (group B) by their troponin levels (MI/ACS - 17.2 plus or minus 23.8 ng/ml versus others - 0.37 plus or minus 0.91 ng/ml, p is less than 0.001).

In the ED, bedside assays of troponins are invaluable tools for the clinician, and their use is cost-effective. However, in the recommended cutoffs levels, only troponin I but not troponin T allowed the safe discharge of patients not requiring acute hospital care.