The findings of this study suggest that the use of ICD-10-CM codes led to better performance than the use of ICD-9-CM codes for identifying people with HBV and HCV. The algorithms performed better in identifying people with HCV than in identifying people with HBV. Of the nine algorithms examined, a gain in PPV complemented with a loss in sensitivity; considering the tradeoff between PPV and sensitivity, the optimal algorithm was ≥2 OP or ≥1 IP codes.
The Centers for Disease Control and Prevention Chronic Hepatitis Cohort Study in the United States used an algorithm of two ICD-9 codes separated by ≥6 months, which had a PPV of 90% for HBV and 92% for HCV.11,12 The PPV of algorithm 2 (≥2 OP codes) in this study was 77% and 88% according to ICD-9-CM and ICD-10-CM, respectively, for HBV and was 91% and 98%, respectively, for HCV.
The better performance of algorithms according to ICD-10-CM than those according to ICD-9-CM is unlikely due to the differences in codes themselves because the classification scheme and number of codes do not differ much between the two revisions. A more likely explanation is the education and training offered by the NHI before the implementation of ICD-10-CM in January 2016, as well as some quality improvement programs later.
Our algorithms exhibited better performance in identifying people with HCV than people with HBV, especially when using ICD-10-CM codes; this was likely because the NHI has covered DAAs for people with HCV since January 24, 2017.19 The physicians were required to provide ICD-10-CM codes for people with HCV for prescribing DAAs.
The performance of our algorithms was better than those of a previous Taiwanese study because of two possible reasons.13 First, we used more data sources (drug prescription, laboratory results, clinical diagnosis) and included a longer study period (2005–2019) than in the previous study (laboratory results for one quarter in 2018). Some of the people with HBV or HCV ICD codes judged as false positive in previous studies might have been judged as true positive in this study because of more evidence. Second, this study was confined to one health care system with three hospitals with relatively high quality of coding, and the previous study covered thousands of hospitals and clinics in Taiwan.
One of the strengths of this study is large sample size. Unlike some previous studies using ICD codes to recruit patients, which allowed only PPV estimation,9,10 in this study, by using systematic sampling, we could also calculate sensitivity. Second, we used a search engine to determine clinical diagnoses through large amounts of electronic medical records. Third, this study is the first to examine the performance of using ICD-10-CM code algorithms to identify people with HBV and HCV. Fourth, we used nine algorithms compared with only one in the previous Taiwan study.
Nevertheless, our study also had several limitations. First, this study was confined to a health care system in southern Taiwan, which might affect the generalization to other populations. However, the main findings (better performance of ICD-10-CM than ICD-9-CM and HCV than HBV) were affected by contextual factors (education and training program and reimbursement of DAA). Therefore, we believe that these conclusions may be applicable to other clinical settings in Taiwan. Second, some of the patients might have positive results of laboratory tests in other hospitals but were not tested in this health care system, rendering them false negatives in this study. Third, similarly, some of the clinical diagnoses recorded by physicians might not be valid.
In conclusion, using the electronic medical records of proportional sampling of 10,000 patients in a health care system in south Taiwan, this study suggests that algorithms using ICD-10-CM codes had better performance than those using ICD-9-CM codes in identifying people with HBV and HCV. Considering the tradeoff between PPV and sensitivity, the optimal algorithm was determined to be as follows: ≥2 outpatient or ≥1 inpatient visits with HBV or HCV ICD codes. Furthermore, ICD codes can better identify people with HCV than people with HBV.