Background <p>The aging global population has led to rising emergency department (ED) visits and hospital admissions among older adults, many of whom have complex medical and social backgrounds. A substantial proportion of these visits may be avoidable, particularly among individuals receiving home medical care. Such avoidable hospitalizations can lead to adverse outcomes such as functional decline and iatrogenic complications, while placing additional strain on healthcare systems. Identifying predictive factors for hospital admission in this population is essential for improving care quality, optimizing resource utilization, and guiding decision-making in prehospital settings.</p> Methods <p>We conducted a retrospective observational study at the Juntendo University Nerima Hospital in Japan. “Tokyo Rule” (TR), a policy enacted on August 1, 2009, by the Tokyo Metropolitan Government, applies to difficult emergency transport cases and mandates that designated hospitals accept unanticipated ambulances. TR criteria included: (1) the patient’s clinical condition was generally moderate or mild; and (2) ≥ 5 medical institutions refused ambulance transfer requests or 20&#xa0;min had elapsed since the selection of medical institutions by an emergency medical technician. If the case meets both criterion (1) and criterion (2), it is regarded as a TR case. Our institution proactively accepts patients transferred by ambulance, including those under TR. Patients aged 75 years or older who were receiving house call medical services at home or in a nursing home (NH) and were transported to our hospital by emergency medical service (EMS) were included in this study. Clinical, demographic, and situational data were obtained from electronic medical records. The primary outcome was hospital admission. Univariate analyses were performed to identify potential predictors, followed by multivariate logistic regression analysis to determine independent predictors. A two-tailed significance level of 0.05 was applied.</p> Results <p>Of the 853 patients transported to our hospital during the study period, 738 met the inclusion criteria. Among them, 503 were admitted, and 235 were discharged from the ED. In the univariate analysis, factors significantly associated with admission included a lower Glasgow Coma Scale score; higher National Early Warning Score; oxygen therapy in the ED; and suspected diagnoses of infection, cerebrovascular disease, or cardiovascular disease. In the multivariate analysis, independent predictors included suspected infection, cerebrovascular disease, cardiovascular disease, digestive disease, oxygen therapy in the ED, and reduced consciousness. Minor trauma and transient loss of consciousness were associated with lower odds of hospital admission.</p> Conclusions <p>This is the first study to identify clinical and situational factors associated with hospital admission among older patients receiving home call medical services at home or in the NH who were transported by EMS. Among these patients, hospital admission was associated with suspected infection; cardiovascular, cerebrovascular, and digestive diseases; oxygen therapy in the ED; and reduced consciousness. These findings may help guide triage and decision-making in emergency care for this vulnerable population.</p>