糖化血色素(Hemoglobin A1c, A1C)已被視為反映病人過去二~三個月血糖控制的最佳長期指標，近年來甚至被建議用以診斷糖尿病，然而，糖化血色素不僅受高血糖持續時間的影響，同時也受到紅血球的壽命及其他干擾糖化血色素檢驗的影響。當糖化血色素被低估，可能造成糖尿病診斷及治療的延誤或不足，以致無法有效避免或延緩糖尿病的併發症；反之，如果糖化血色素被高估，則可能造成過度的治療，而引發低血糖的危害。我們將提出臨床病例來說明這些狀況，並加以討論。
　　Hemoglobin A1C has been used as the best long-term indicator of glycemic control in the past two to three 3 months for decades, and even recommended as a convenient parameter for diagnosing diabetes in recent years. However, the reliance on the A1C as a parameter to diagnose diabetes mellitus and to monitor glycemic control was influenced not only the duration of glycaemia, but also the lifespan of red blood cell and other conditions that interfere the accurate estimation of hemoglobin A1C. When the hemoglobin A1C is underestimated, diagnosis and/or treatment of diabetes would potentially be delayed or suboptimal. On the other hand, if the hemoglobin A1C is overestimated, improper treatment would potentially jeopardize the patient with the complication of hypoglycemia. Clinical cases with different conditions that make hemoglobin A1C not reliable in practice will be demonstrated and discussed.