Objective:To investigate the predictive value of serum D-dimer combined with myocardial injury markers on admission for early identification of high-risk patients with acute myocarditis.Methods:Patients hospitalized for acute myocarditis in China-Japan Friendship Hospital were retrospectively enrolled from 2010 to 2021. Patients were divided into the high D-dimer level group and low D-dimer level group according to the median value of D-dimer measured by immunoturbidimetry within 24 h of admission. In-hospital adverse events were defined as death, cardiogenic shock, malignant ventricular arrhythmia and new-onset heart failure. Multivariate logistic analysis was used to explore the independent predictors of in-hospital adverse events, and receiver operating characteristic curve was used to evaluate the predictive value.Results:A total of 106 patients were analyzed, including 52 high level D-dimer patients and 54 low level D-dimer patients, with an average age of (36±16) years, and 62.3% were male. Compared with the low D-dimer level group, patients in the high D-dimer level group had lower mean systolic blood pressure [(114±21) mmHg vs. (121±14) mmHg] and diastolic blood pressure [(71±13) mmHg vs. (76±10) mmHg], higher heart rate [(97±26) beats/min vs. (79±15) beats/min], higher C-reactive protein levels [6.82 (1.61, 20.05) mg/dL vs. 1.30 (0.13, 8.93) mg/dL] and creatinine levels [86.95 (67.63, 117.83) μmol/L vs. 68.80 (60.18, 81.93) μmol/L] on admission. The proportion of patients having QRS interval >120 ms on electrocardiogram was higher in high D-dimer level group (25.0% vs. 7.4%). There was no significant difference in patients with positive myocardial injury biomarkers between the two groups. The incidence of in-hospital adverse events was higher in the high D-dimer level group (67.3% vs. 22.2%, P<0.001). Multivariate logistic analysis showed that serum D-dimer levels and elevated myocardial injury markers on admission were independently associated with in-hospital adverse events. The area under the curve (AUC) of elevated serum D-dimer level on admission for predicting in-hospital adverse events was 0.781 (95% CI: 0.690-0.873), the sensitivity was 74.5%, and the specificity was 71.2%. When combined with positive cardiac biomarkers, the AUC was 0.831 (95% CI: 0.752-0.910) with a sensitivity of 80.9% and a specificity of 78.0%. Conclusions:Elevated D-dimer level on admission can predict the risk of in-hospital adverse events in patients with acute myocarditis. The combination of cardiac injury biomarkers can improve the predictive value.