# A Blockchain-Applied Personal Health Record Application: Development and User Experience
###### Abstract  
This study aims to introduce a novel blockchain-applied personal health records (PHR) application and validate its user experience. The system transmits the part corresponding to the patient's personal information off-chain and prevents data forgery and falsification by storing encrypted data on-chain. Patients may easily trace the opt-in and opt-out history of their consent data and dynamically store the consent system for data exchange on the blockchain. A mixed-method study using a questionnaire, in-depth interviews, and usability evaluation were conducted for 30 participants. The system usability score was 74.0, indicating the high usability of the application. Those who were familiar with blockchain showed confidence in the application, but those unfamiliar wanted their data to be safe using another way. Most of the participants were interested in exchanging and using their medical data and considered security important but those unfamiliar wanted their data to be safe using another way. We found that participants were concerned about data security and considered a blockchain-based PHR as a novel way to store and exchange their medical information securely. Blockchain is not a visible technology. However, a blockchain-applied PHR must be able to win user trust through visualizations, certificates, and system descriptions. medical informatics applications; blockchain; health records; personal addressref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,ref=affiliation,refiliation,ref=aff  
Security and reliability are important factors in medical data and PHRs. A study on PHR recognition by medical staff also showed skepticism about inaccurate data and security issues [8]. There are some possible threats, such as data loss and data manipulation, which could undermine trust in the patient-centered system. Blockchain is an emerging technology to solve these dilemmas, guaranteeing transparency, decentralization, and immutability of the system [9]. Some studies have explored blockchain technology in the healthcare domain. Platforms, such as OmniPHR, MedRec, and FHIRChain are used to transform patient health data sharing in a patient-centric manner [10; 11; 12]. Blockchain has also been used to share and store clinical trial data, manage healthcare-related Internet of things, detect medical and research fraud, and conduct public health surveillance [13; 14; 15]. In the case of consent data among medical information, data are scattered by institution, and decisions can vary according to each patient's point of view, so a convenient way to safely manage and reflect the dynamic consent system is needed. Although it is an important component in blockchain-applied PHRs, there are few studies related to user experience. Most studies related to blockchain-applied PHRs have tended to focus on blockchain technology. [PERSON] et al. used a multichain platform with electronic hospital record (EHR) data to share health data and improve audit logging securely [16]. [PERSON] et al. used a private blockchain with medical image records to securely share patient medical images, but data search was not considered [17; 18]. [PERSON] et al. used a hybrid consensus mechanism based on practical Byzantine fault tolerance but failed to provide sufficient privacy for the patient's identity and energy efficiency [19; 20]. [PERSON] et al. used the Ethereum platform to manage EHR data in a cloud environment, but despite high scalability, it was not practically feasible [21]. [PERSON] et al. used the Hyperledger platform to manage personal data in e-health, but there was no access control or exhaustive authorization consideration [22; 23; 24]. The aim of this study was to introduce a novel blockchain-applied PHR application and to validate its user experience. Thus far, existing research has focused on the technical aspects of blockchain-applied PHR.