## 4 Discussion
Even though there were several limitations, as we mentioned above, FirstER is well-designed and developed for our initial purpose. The usability of this prototype may be expanded by having more participating hospitals, containing admission records, and having other medical data, such as radiological examinations. Moreover, further updates would focus on covering detailed data on chronic medical illnesses and recent emerging infectious diseases. Research about the validity and reliability of FirstER has been progressing in another study with survey analyses from both healthcare providers and patients. It is promising that FirstER has already been downloaded more than 1000 times, and most responses to questions about usability in the pilot surveys have shown user satisfaction. Meanwhile, dissatisfaction, because the app was hard to use the first time, was one of the most common answers on the surveys, especially for those patients who were not familiar with using a smartphone. After developing FirstER and installing the app on a user's device, there were some cases in which the app did not work due to conflicts between the app and certain versions of mobile phones. Most such problems were solved by stabilizing the cloud server and updating the app. However, the app did not work in very remote versions in a few mobile phones despite continuously updating the app. Furthermore, the patients need to follow multiple steps with many instances of giving informed consent to provide their records to physicians. These complicated processes are largely to protect the patients' privacy; however, involving patients' caregivers to introduce manuals for the app and further updates would improve usability. With the developing platform for the mPHR, ED physicians could diagnose and treat their patients more quickly and efficiently, because problems similar to previous ones could be solved without duplicated tests. Fewer clinical tests due to decreased duplicated tests might have a positive effect on improving overcrowding in EDs, though this needs further evaluation. Previous studies reported that the turnaround time for laboratory and radiologic tests negatively impacts ED overcrowding and length of stay [21; 22]. Improving the quality of care and enhancing the safety of patients is multifactorial, and one of the most effective ways to diminish overcrowding can be by avoiding unnecessary laboratory and imaging examinations [23]. Future studies need to focus on which information on the PHRs can improve patient outcome. Also, research on PHR-based emergency medical services can further progress by expanding the mobile app. Categorizing the data provided, it was found that the app users requested their laboratory results in addition to the visit data that are provided by default. We noticed several limitations while developing and applying FirstER. First, the patients' usability and satisfaction might be lower than expected because a relatively small number of hospitals participated. If the clinical data could be connected between tertiary hospitals and primary clinics, the app's usability would be improved. For example, patients with mild infectious illnesses or simple minor trauma cases could provide their laboratory results and prescriptions to their primary healthcare provider through this app after adequate treatment in the emergency department. However, FirstER is the first platform in an emergency to support interoperability between hospitals, and further study could make it possible to share PHRs at many hospitals. Second, data for radiologic examinations, such as simple radiographs, computed tomography, and magnetic resonance imaging, could not be provided because of limited storage and bandwidth. Third, there were some reports of errors during the uploading and downloading of data in the mobile app. These errors were mostly because of the different existing platforms between hospitals and different data types with test codes.