目標：探討週日使用西醫醫療資源的患者特質，並探討病人特性、醫事機構特性及院所週日門診開診狀況對忠誠病人急診利用之影響。方法：本研究採用健保資料庫，研究期間為2016 年至2018年，以有固定就醫院所之病患為主要研究對象，使用羅吉斯迴歸分析「固定就醫院所週日開診狀況」、「病人特性」、「醫療利用」、「醫事機構特徵」對忠誠病人選擇門診或急診醫療之影響。結果：研究結果顯示男性、65歲以上的老人、低收入戶、有共病症、有重大傷病、身心科就醫病史、門診就醫次數低、有住院的紀錄、就醫時間越晚、就醫科別為外科、兒科、忠誠院所特約層級別越高、就醫院所位於高度都市化市鎮者、忠誠院所位於低度都市化市鎮者、開診率較低的醫療區更容易至急診就醫，在控制其他變項後，院所週日未開診則其忠誠病人至急診的風險顯著高於有開診的院所（OR=12.72，95%CI：12.56-12.87）。結論：研究顯示院所週日開診與否與其忠誠病人急診利用相關，因此建議衛生主管機關除提供誘因鼓勵假日開診外，強化基層醫療照護系統、宣導民眾應用資訊科技，提升資料查詢便利性及正確性，使西醫基層醫療照護的可及性及可近性提高，促進醫療資源有效利用，以減少假日急診壅塞情形。

Objectives: Barriers to timely access to usual sources of medical care lead patients to use the emergency department as a ready alternative. This study aims to determine the characteristics of patients who use medical resources on Sundays. We also examined the relationship between emergency department visits and barriers to receiving usual sources of care in a timely manner for loyal patients. Methods: Data from 2016 to 2018 were obtained from Taiwan’s National Health Insurance Research Database, and the study estimated of medical care utilization in the past year. Patients were classified as having a usual source of care if they made 80% or more of their total ambulatory visits to the same clinic. Descriptive statistics and logistic regression analyses were used to determine relationships between the medical service provided on Sundays and the use of the emergency department by loyal patients. Results: This study included 2,952,002 ambulatory and emergency department visits from 1,449,968 loyal patients. Patients who had a higher risk of emergency visits had the following characteristics: male, over 65 years of age, low-income, co-morbidities, major injuries, poor physical health, or poor mental health. In terms of medical use, the following was also associated with a higher risk of emergency visits by patients: low outpatient visits, having a record of hospitalization in the past year, after-hours visits, medical needs for surgery, or pediatrics. The positive associations between barriers to receiving usual source of care in a timely manner and emergency department usage persisted even in multiple logistic regressions that adjusted for patient characteristics, medical use, and characteristics of medical institutions. The risk of emergency department visits was significantly higher among loyal patients whose usual clinics did not provide medical services that met their needs than among patients whose usual clinics did meet their needs (OR=12.72, 95%CI:12.56-12.87). Conclusions: The results indicate that loyal patients who have barriers to their usual source of medical care are more likely to utilize the emergency department. Improving the availability and accessibility of primary medical care on Sundays may help reduce rates of emergency department use and resolve current situations of unmet medical needs.