Supplementary Material for: Regional variation in the use of percutaneous kidney biopsy in Japan

Introduction: The regional variation in the use of percutaneous kidney biopsy in Japan remains unknown. There are several large datasets of kidney biopsies in Japan, but an exhaustive survey of kidney biopsies is lacking. Methods: We analyzed insurance claims for percutaneous kidney biopsies registered in the National Database of Health Insurance Claims and Specific Health Checkups of Japan, which is the closest to a complete dataset of kidney biopsies performed in Japan. In combination with other nationwide survey results, the number of inpatient percutaneous kidney biopsies per population in each prefecture was calculated. Factors associated with the frequency of percutaneous kidney biopsies were also explored. Results: The database contained 22,419 health insurance claims for percutaneous kidney biopsy in the fiscal year 2020. The frequency of inpatient percutaneous kidney biopsies could be up to 4.8 times as frequent in one prefecture than in another, even after adjusting for age and sex. The frequency of inpatient percutaneous kidney biopsies showed a positive correlation with the number of annual kidney transplants and patients on peritoneal dialysis per population and a weak negative correlation with the prevalence of reduced kidney function in the population aged 40–74 years. Conclusion: We found a large regional variation in the frequency of inpatient percutaneous kidney biopsies. Kidney transplants and peritoneal dialysis might be offered more frequently in regions with a higher frequency of kidney biopsy. This is the first dataset that shows more than 20,000 kidney biopsies were performed per year in Japan, as of 2020.

研究背景：日本经皮肾活检（percutaneous kidney biopsy）的临床应用地区差异尚不明确。目前日本已有多项肾活检相关大型数据集，但仍缺乏针对肾活检的全面系统性调查。研究方法：本研究分析了日本国民健康保险索赔与特定健康检查数据库（National Database of Health Insurance Claims and Specific Health Checkups of Japan）中登记的经皮肾活检保险索赔数据，该数据集是目前日本境内最接近完整肾活检执行情况的数据集。结合其他全国性调查结果，本研究计算了日本各都道府县每常住人口对应的住院经皮肾活检数量，并探讨了影响经皮肾活检开展频率的相关因素。研究结果：该数据库收录了2020财年共计22419条经皮肾活检健康保险索赔记录。即便校正年龄与性别因素后，部分都道府县的住院经皮肾活检开展频率最高可达其他都道府县的4.8倍。住院经皮肾活检开展频率与每常住人口年度肾移植例数、腹膜透析患者数呈显著正相关，与40~74岁人群肾功能减退患病率呈弱负相关。研究结论：本研究证实日本住院经皮肾活检开展频率存在显著地区差异。肾活检开展频率较高的地区，肾移植与腹膜透析服务的供给可能更为频繁。截至2020年，本数据集是首个公开显示日本年肾活检执行量超20000例的数据集。