Background <p>High-sensitivity cardiac troponin I assays enable early exclusion of myocardial infarction in the emergency department. However, the clinical implications of detectable troponin values below the 99th percentile upper reference limit (4–18 ng/L) remain unclear.</p> Objective <p>To assess the association between subthreshold troponin levels and 30-day outcomes in patients from the RACE-IT trial, using exact troponin values when available.</p> Methods <p>This post-hoc analysis of the RACE-IT stepped-wedge randomized controlled trial included patients with troponin ≤ 18 ng/L across nine EDs. Patients were stratified by initial troponin, peak value, absolute change, and percent change. The primary outcome was a 30-day composite of all-cause death, acute MI, percutaneous coronary intervention, and coronary artery bypass grafting. Logistic regression analysis after adjusting for age, sex, race, and coronary artery disease was performed.</p> Results <p>Among 19,194 patients with troponin ≤ 18 ng/L, 117 (0.6%) experienced the composite outcome. Higher troponin levels were associated with increased event rates in unadjusted analyses. Adjusted analyses showed no independent associations overall, though patients whose highest troponin values fell within the ≥ 11– ≤ 18 ng/L range continued to demonstrate significantly worse outcomes than those with lower peak levels. Elevated troponin values correlated with older age, male sex, and greater comorbidity burden.</p> Conclusion <p>In this post-hoc analysis of patients with troponin values below the 99th percentile URL, absolute levels and temporal changes were not independently associated with 30-day adverse outcomes. These findings support the use of subthreshold troponin values in rapid rule-out protocols, emphasizing the need to consider clinical context and comorbidities in risk assessment.</p> Graphical Abstract <p></p>