Seasonal and Time-of-Day Variations in Ambulance-Transported Emergency Department Diagnoses: A One-Year Observational Study.

Background/Objectives: Ambulance-transported patients represent an important subgroup of emergency department (ED) admissions and may demonstrate distinct temporal presentation patterns. However, studies simultaneously evaluating broad diagnostic categories according to both time-of-day and seasonal variations among ambulance-transported patients remain limited. Methods: This retrospective observational study included 37,188 patients transported to the emergency department of a tertiary university hospital by ambulance between December 1, 2024, and November 30, 2025. Patients were categorized into twelve major diagnostic groups according to ICD-10-based clinical diagnoses. Temporal analyses were performed according to seasons and time-of-day intervals (nighttime, daytime, and evening). Associations between diagnostic categories and temporal variables were evaluated using chi-square analysis. Results: Trauma was the most common diagnostic category (19.9%), followed by cardiovascular (16.3%), gastrointestinal (10.3%), and respiratory diseases (10.1%). Significant associations were observed between diagnostic categories and both seasonal distribution (χ2 = 446.482, df = 33, p < 0.001) and time of presentation (χ2 = 642.883, df = 22, p < 0.001). Respiratory diseases were most frequent during winter (32.7%), whereas trauma-related admissions peaked during summer (32.4%). Psychiatric presentations predominantly occurred during evening hours (53.2%), while gastrointestinal diseases demonstrated the highest proportion of nighttime admissions (24.2%). Trauma-related admissions were more common among males (63.6%), whereas neurological, gastrointestinal, metabolic, and psychiatric presentations were slightly more frequent among females. The mean age of the cohort was 49.02 ± 25.12 years. Conclusions: Ambulance-transported emergency department patients demonstrate significant seasonal and time-of-day variations across major diagnostic categories. Awareness of these temporal patterns may contribute to improved emergency department organization, ambulance deployment, staffing strategies, and healthcare resource management.