How to Interpret Elevated Cardiac Troponin Levels
Cardiac troponin (cTn) testing is an essential component of the diagnostic workup and management of acute coronary syndromes (ACS). Although over the past 15 years the diagnostic performance of the previous gold-standard assay, creatine kinase-MB, has not changed appreciably, the ever-increasing sensitivity of cTn assays has had a dramatic impact on the use of cTn testing to diagnose ACS.1 Here, we present 3 recent clinical cases from the emergency department with acute chest discomfort that exemplify the challenges introduced by high-sensitivity cTn assays: a 48-year-old man who presented to the emergency department with chest discomfort lasting 2 hours and a 3-day history of flu-like symptoms whose ECG showed diffuse ST-segment changes, a 60-year-old woman with a medical history of heart failure who presented to the emergency department with chest pain lasting 1.5 hours whose ECG was nondiagnostic, and a 54-year-old man with a medical history of diabetes mellitus who presented with chest discomfort lasting 1 hour whose ECG was normal.
Cardiac troponin I (cTnI) testing (TnI-Ultra assay on the ADVIA Centaur XP immunoanalyzer, both Siemens Healthcare Diagnostics) was ordered on all 3 patients. The laboratory results were reported as positive in all 3 cases, with the reported values being 0.05, 0.06, and 0.06 ng/mL, respectively, all just above the diagnostic limit of 0.04 ng/mL.
Assays for cTn, namely cTnI and cardiac troponin T (cTnT), are the preferred diagnostic tests for ACS, in particular non–ST-segment–elevation myocardial infarction, because of the tissue-specific expression of cTnI and cTnT in the myocardium. The results of cTn testing often guide the decision for coronary intervention. However, although the increasing sensitivity of cTn assays lowers the number of potentially missed ACS diagnoses, it presents a diagnostic challenge because the gains in diagnostic sensitivity have inevitably come with a decrease in specificity. For instance, the replacement …