The lifespan of a red blood cell is around 100-120 days, which means that the red blood cell is released from the bone marrow and the red blood cell apoptosis takes place in about 100-120 days. Because of this, the lifespan of red blood cells is one of the longest-lived types of all blood cells. Because of the long lifespan of red blood cells, one indicator that is often used in clinical practice to determine the body’s blood glucose level is glycated hemoglobin. Glycated hemoglobin is a substance formed by the slow oxidation of glucose hemoglobin in the blood, and it is not affected by other factors and its value is very stable. In other words, it reflects the patient’s blood glucose level over a period of about 100-120 days prior to the measurement. Because of this, the measurement of glycated hemoglobin is a valuable reference for understanding the patient’s preexisting blood glucose level.