Erroneous diagnosis of COVID-19 mRNA vaccine-associated acute myocarditis due to false-positive high-sensitive troponin I assay: a case report.

Background: Coronavirus disease 2019 (COVID-19) mRNA vaccine-associated acute myocarditis has been well described, and the demonstration of elevated high-sensitivity cardiac troponin (hs-cTn) is crucial for its diagnosis. However, falsely elevated hs-cTn can occasionally occur, leading to incorrect diagnosis. Here, we report the case of a patient who was given an erroneous diagnosis of COVID-19 mRNA vaccine-associated acute myocarditis due to falsely elevated hs-cTn, likely from assay interference. Case summary: A 29-year-old Chinese male presented with 3 months of chest pain, dyspnoea, and palpitations starting a few days after his second dose of mRNA-1273 (Moderna) vaccine. High-sensitivity cardiac troponin I was elevated at presentation, which rose further 4 h later. The provisional diagnosis was acute myocarditis after a computed tomography coronary angiogram showed normal coronaries. Cardiac magnetic resonance was also negative for myocardial inflammation. The hs-cTn I levels fluctuated but remained elevated on outpatient serial testing, despite no new symptoms or clinical events. A paired serum sample showed elevated hs-cTn I but normal hs-cTn T, confirming a diagnosis of false-positive hs-cTn I. Further investigations, including blood tests before and after a subsequent uneventful mRNA-1273 booster vaccination, were performed to investigate for assay interference. Discussion: Widespread COVID-19 mRNA vaccination has resulted in an awareness of vaccine-related acute myocarditis and a more thorough evaluation of post-vaccination cardiac symptoms. Although false-positive hs-cTn rarely occurs, extensive testing will inevitably result in a significant number of patients with falsely elevated hs-cTn. Clinicians should exclude this possibility and consider using alternative hs-cTn assay when investigation results and clinical presentation appear discordant.