P1490MONTHLY TREND AND SEASONALITY IN ACUTE AND CHRONIC HEMODIALYSIS; RESULT FROM NATIONWIDE DATABASE OF MEDICAL BILLS OF UNIVERSAL HEALTH CARE INSURANCE SYSTEM IN JAPAN
Authors: Tsunoda Ryoya , Kai Hirayasu , Kondo Masahide , Mitsutake Naohiro , Yamagata Kunihiro 
Published: June 2020

Abstract

Background and Aims
Although knowing the accurate number of patients of hemodialysis important, data collection is a hard task. Establishing a simplified and prompt method of data collection for perspective hemodialysis is strongly needed. In Japan, there is a universal health care insurance system that covers almost all population. This study aimed to know a seasonal variation of hemodialysis patients using the big database of medical bills in Japan.

Method
Japanese Ministry of Health, Labour and Welfare established a big database named National Database (NDB), that consists of medical bills data in Japan. All bills data were sent to the data server from The Examination and Payment Agency, the organization that receives all medical bills from each medical institution and judge validity for payment. Each record of the database consists of bill data of one patient of a month for each medical institution. All data were anonymized before saved in the server and gave virtual patient identification number (VPID) that is unique for each patient. VPID is a hash value calculated by patient’s individual data such as name, date of birth, so that the value cannot be duplicate. Calculation of VPID is executed by an irreversible way to make it difficult to decrypt VPID into patient’s individual data. This database includes all information about medical care of whole population in Japan except for patients not under the insurance system (patients under public assistance system, victims of the war, or any other specified people under the public medical expense).
Using this database, we investigated monthly number of patients who were recorded to be undergone hemodialysis (HD, includes hemodiafiltration). We searched chronic HD patients who have undergone HD on the month and continued it for 3 months, and acute HD patients who have discontinued HD within 3 months.

Results
In NDB, the number of chronic HD patients under public insurance system who confirmed to have undergone HD in December 2014 was 284 433. In contrast, the number of HD patients identified from the year-end survey by Japanese Society of Dialysis Therapy in the same year was of 311 193, but this number includes patients not under insurance system. Incidence rate of acute HD in Japan was persisted at 30-39 per million per month. There is a reproducible seasonal variation in number of acute HD patients, that increases in every winter and decreasing in every summer. The significantly highest frequency was observed in February(38.5/million/month) compared with September(30.6/million/month), the lowest month of the year (p&lt;0.01).

Conclusion
We could show the trend in number of HD patients using nationwide bills data. Seasonality in some clinical factors in patients under chronic hemodialysis such as blood pressure, intradialytic body weight gain, morbidity of congestive heart failure, and, mortality, has been reported in many observational studies. Also, there are a few former reports about seasonality in AKI. However, a report about acute RRT is few. From our knowledge, this is the first report that revealed monthly dynamics of HD in a whole nation and rising risk of acute HD in winter. The true mechanism of this seasonality remains unclear. We have to establish a method to collect clinical data such as prevalence of CKD, causative diseases of AKI, kinds of precedent operations, and medications in connection with billing data.