In this study, we used nationwide claim data collected over 15 years to investigate the epidemiological characteristics of AILD. The prevalence of AIH, PBC, and PSC were 18.4, 11.8, and 1.5 per 100,000 population, while the corresponding incidence was 2.3, 1.4, and 0.3 per 100,000 population, respectively, in 2019. The 10-year survival rates were 89.8%, 74.9%, and 73.4%, respectively. This result reflects the clinical significance of AILD in Korea.

In our study, more than half of AILD patients are diagnosed in middle to late age. Most AIH and PBC patients were diagnosed in their fifties or sixties, while the age at diagnosis for PSC was spread more evenly between the age range of 50-80 s. AIH and PBC showed female dominancy (84.0% and 83.3% female patients, respectively), while PSC was not gender dependent (49.4% female patients). The age at the initial diagnosis and female predominance of AIH (76–80% of females with a median age of 43–68 years) and PBC (54-86.5% of females with a mean age of 52.8–64.7 years) are similar to the findings of other studies [18, 20,21,22,23]. However, the demographics of the PSC population differed from previous studies, which generally showed that PSC was diagnosed in middle age (median age of 35–55 years) with male predominancy (55–75%) [22,23,24,25]. This difference might be attributed to the epidemiological variations in the disease entity or the higher probability of detecting laboratory abnormalities in individuals aged 20 years or older who undergo national healthcare checkups every two years [31].

Previous epidemiology studies about AILD are few and incomplete with considerably different results. The prevalence of AIH ranges from 4.0 to 42.9 per 100,000 population, and the incidence ranges from 0.5 to 3.0 per 100,000 population per year [13,14,15,16,17]. Those of PBC were 10.0 to 58.1 and 0.78 to 5.23 per 100,000 population per year, respectively [18,19,20,21]. Likewise, the prevalence and incidence of PSC ranged from 1 to 16.2 and 0.04 to 1.3 per 100,000 population per year, respectively [6, 22,23,24,25]. These discrepancy are based on the study limitations; for example, some were only hospital or community-based and used ambiguous disease definitions [7]. Epidemiological studies of rare diseases should be population-based to avoid non-random selection bias. The diagnostic criteria must adhere to international disease definition based on clinical results. The results must be standardized to eliminate innate bias from regional and demographical differences. With these considerations in mind, our results reflect unbiased and reproductive real-world data on AILD with comparability to other studies.

Our results show that the number of newly diagnosed AILD patients in Korea has been increasing since 2010, as has the sex-age-standardized incidence of AIH and PBC. The total number of patients newly diagnosed with AIH was 507 in 2010 and 1,169 in 2019. In the case of PBC, the numbers were 271 and 724 for the respective years.

The sudden increase in the number of AILD patients in the early days may have been influenced by the health and welfare policy. AILD patients who were previously diagnosed and treated would be enrolled as RID patients in the early days of the RID policy, which began at once as is true for PSC in 2014. The prevalence of AILD has also increased rapidly over time. The cumulative number of AILD patients has been rising.

The AILD diagnosis and care is challenging [1, 3, 4, 6]. In our study, the duration of AILD confirmation (initial KCD code to RID code date for AILD) took about 3.7 to 20.7 months. AILD diagnosis needs to exclude other liver diseases caused by viral, drug, or hereditary diseases, and, sometimes, requires pathologic confirmation. The demand for medical facility use was mostly focused on the first year of diagnosis and decreased from the second year. Previous studies have shown that the 10-year survival rates of AIH, PBC, and PSC were 82–91%, 38–94%, and 64–92%, respectively [18, 32,33,34,35]. In our study population, the 10-year survival rates of AIH, PBC, and PSC were 89.8%, 74.9%, and 73.4%, respectively.

The strength of this study is the use of a nationwide cohort with almost 100% coverage of the Korean population over a long period of time. However, there are some limitations. First, due to the inherent limitations of claims data, we could not retrieve medical records, making it impossible to assess the clinical finding such as laboratory, image, or histological results. Thanks to RID system, our data is accurate and reliable overcoming potential confounding biases. The sensitivity and specificity of ICD-10 code with RID code in other rare disease were 92–98% [36]. Also, we applied the same diagnostic criteria for AIH, PBC and PSC, it reveals the trend of AILD. In this study, we mainly focused on the epidemiology of AILD and did not collect other medical conditions that might affect AILD. We plan to further investigate comorbidities, liver functions, or malignancies which might affect clinical course of AILD. Lastly, we were not able to reveal the reasons of medical use in this study. The hospital utilization were most frequent in the first year of diagnosis. Patients with AILD might either present with the early stage of the disease without significant liver dysfunction for some period under proper management, or with the end stage of liver disease requiring ER visit or ICU admission. More specific data regarding the reasons for medical utilization in the long term is required to understand better about the clinical presentation of AILD.

In conclusion, this nationwide study demonstrated the epidemiology of AILD in Korea. This information will facilitate the understanding of AILD using a real-world database. As the incidence and prevalence of AILD increases, further studies to improve the overall well-being of AILD patients are warranted.