## 4 Discussion  
In this study, we introduced a newly developed mobile app, called FirstER, which enables the aggregation of data from three hospitals and yields PHRs to others if needed. Even though FirstER needs further validation, it demonstrates that mobile apps can enable interoperability between different sources of PHRs from different hospitals. Medical record interoperability has been recognized to improve convenience and clinical outcomes for patients. With the rapid uptake of smartphones and the digitalization of medical records, healthcare services have planned the development of mobile health apps. [PERSON] et al. previously introduced a mobile application to provide diabetes self-management, including cardio-cerebrovascular risk evaluation, stress evaluation, and an exercise tutor [14]. [PERSON] et al. evaluated the usefulness of PHRs for patients with hypertension and concluded that they might have a limited impact. However, these studies focused on non-emergency situations [15]. One pilot study announced the development of a mobile emergency app to improve interoperability between pre-hospital services and hospitals in a mass-casualty situation [16]. Although this application might be useful for emergency physicians, it was not intended for patients. To the best of our knowledge, FirstER is the first mobile app prototype for patients who visit the ED and use their PHRs at other hospitals in an emergency. Whenever patients unintentionally first visited nearby hospitals, FirstER enabled medical personnel to know about the patients' previous underlying diseases, the reasons why they visited other hospitals, and what they were prescribed [17]. Furthermore, we also enabled patients to input their health records (i.e., patient-generated health data), such as conditions and blood pressure results, into FirstER, which then provided physicians with these data to help understand patients' conditions [18]. Using wearable devices with FirstER could provide more expansive and diverse datasets to help clinicians with decision-making about care plans [19; 20]. In this investigation, we focused on variables that are commonly useful for emergencies by analyzing the frequencies of prescriptions. Furthermore, emergency medicine physicians discussed with each other the clinical importance of the variables and reached a consensus on which ones to include. The parameters needed to be reliable, accurate, and easy to access. Regarding the selection of such parameters, we considered numerous issues. At first, we attempted to insert radiologic examinations, which could be helpful for efficient diagnosis and treatment. Nevertheless, the final \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Category of EMR-Tethered Data Provided** & **Samsung Medical Center** & **Asan Medical Center** & **Dong-A University Hospital** & **Total (\%)** \\ \hline Visit & 4523 & 1694 & 2398 & 8615 (54.0) \\ Consultation history & 16 & 0 & 0 & 16 (0.0) \\ Laboratory test & 2699 & 886 & 1636 & 5221 (32.7) \\ Operation history & 10 & 0 & 2 & 12 (0.0) \\ Prescription data & 1285 & 241 & 561 & 2087 (13.1) \\ Total & 8533 & 2821 & 4597 & 15,951 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Frequency of system access and utilization. Numbers indicate counts of EMR-tethered data provided during the study period. version of the app did not contain such data because of storage and bandwidth issues. Radiologic reports without images were not provided because these frequently mislead both patients and physicians. Secondly, we also did not include the results of bacterial or viral cultures, including those for multi-resistance bacteria, sexually transmitted diseases, or new emerging infections. We thought that hiding such data could be problematic in specific situations. However, after reviewing Korean Privacy Act issues, we decided to exclude sensitive health records, including those relating to sexually transmitted diseases. This was largely because there tends to be a stigma in our country around revealing delicate past medical histories.