Validation of ICD-10-CM diagnosis codes for identifying COVID-19 cases using administrative claims data in Taiwan

BACKGROUND: Accurate identification of COVID-19 cases is essential for real-world studies. This study assessed the validity of ICD-10-CM code U07.1 for identifying COVID-19 cases in administrative claims data in Taiwan. METHODS: This observational validation study linked National Health Insurance claims with laboratory-confirmed SARS-CoV-2 RT-PCR results from a multi-institutional database. We included 127,300 outpatient, emergency, and inpatient encounters from 2022. Positive and negative predictive values (PPV, NPV), sensitivity, and specificity were calculated using RT-PCR results as the reference standard, with stratified analyses conducted by clinical setting, time period, patient demographics, and hospital level. RESULTS: Overall, the U07.1 code demonstrated high PPV (95.3%) and specificity (99.5%), but moderate NPV (77.9%) and low sensitivity (26.6%). While PPVs remained consistently high across all clinical settings (> 91%), NPVs varied significantly, being lowest in outpatient visits (41.3%). Temporally, NPV and sensitivity were lowest during April-June 2022 (57.7% and 14.9%, respectively), coinciding with the peak outbreak and the transition toward antigen-based diagnostic policies. Sensitivity was markedly higher among inpatients (84.4%) and older adults aged ≥ 80 years (60.5%) compared to younger populations. CONCLUSION: ICD-10-CM U07.1 is a highly reliable marker for identifying confirmed COVID-19 cases in Taiwan's claims data. However, the low overall sensitivity and substantial variability in NPV suggest significant under-capture of mild infections, particularly in outpatient settings. Researchers should exercise caution when using this code to estimate total disease burden or when defining code-negative control cohorts.