Positive Predictive Value of ICD-10-CM Codes for Myocarditis in Claims Data: A Multi-Institutional Study in Taiwan

Purpose: The validity of the diagnosis codes to identify myocarditis cases in healthcare databases research remains unclear, and this study aimed to determine the coding accuracy of myocarditis in Taiwan.Methods: We conducted a cross-sectional study based on Taiwan's largest multi-institutional healthcare system to identify inpatients newly diagnosed with ICD-10-CM myocarditis codes at discharge between January 1st, 2017 and March 31st, 2022. We ascertained the myocarditis diagnosis by a gold standard biopsy or by review of electronic medical records, and the positive predictive values (PPV) with 95% confidence intervals (CI) of the ICD-10-CM codes for myocarditis were determined.Results: We included a total of 498 inpatients (mean age: 33.8 years old; female: 38.8%) with new myocarditis diagnosis at discharge. Codes I409 (30.1%) and I514 (45.4%) constituted the majority of myocarditis diagnostic codes in any coding position, and the overall PPV of the myocarditis codes was 73.5% (95% CI: 69.6-77.4%). However, the highest PPV (96.6%) for myocarditis diagnosis was noted with code I409 as the primary diagnosis. We found 132 inpatients (26.5%) who were false-positive myocarditis cases, identified by the ICD-10-CM codes, and potential reasons for misclassification included other inflammation diseases (n=35, 26.5%), pre-existing heart failure (n= 25, 18.9%) and acute myocardial infarction (n=16, 12.1%).Conclusion: The PPV of ICD-10-CM codes for myocarditis in Taiwan was acceptable, but some other inflammation diseases and pre-existing heart diseases may be falsely coded as myocarditis. Our results may serve future secondary database studies as a fundamental reference on the validity of myocarditis diagnosis codes.