Glycosylated hemoglobin (GHb) is the product of a slow, continuous reaction between hemoglobin (HbA) and hexose (mainly glucose) in red blood cells, and the rate of this reaction is proportional to the concentration of glucose; because this reaction is irreversible, once produced, it is chemically very stable and not affected by fluctuations in blood glucose; the life span of red blood cells is usually 90 days (3 months), and GHb is not affected by fluctuations in blood glucose. It is only after the destruction of red blood cells that glucose dissociates from hemoglobin, so GHb reflects the average blood glucose level for the past 3 months. Due to the different sugar molecules bound by hemoglobin (HbA), GHb is divided into HbA1a, HbA1b and HbA1c, of which HbA1c has the highest content and is significant for high blood glucose, especially when blood glucose fluctuates greatly. Because glycated hemoglobin is affected by many factors (race, age, gender, and hemoglobin level), there is still controversy around the world about the cut point value of glycated hemoglobin for the diagnosis of diabetes, and the current reference to our 2017 diabetes guidelines sets the cut point value of glycated hemoglobin at 6.5%.
The clinical significance of glycosylated hemoglobin: 1. The higher the glycosylated hemoglobin value, the less well-controlled the blood glucose; 2. Glycosylated hemoglobin is closely related to various complications of diabetes (retinopathy, nephropathy, neuropathy); 3. Fasting blood glucose and postprandial blood glucose each dominate at different levels of HbA1c, which is important for glucose control treatment of diabetes.
Cautions about measuring glycosylated hemoglobin: 1. Glycosylated hemoglobin reflects the average blood glucose level over 3 days and does not reflect the true blood glucose level if the blood glucose fluctuates too much; 2. It is affected by some diseases, such as some kidney diseases, hemolytic anemia, etc. Glycosylated hemoglobin also does not reflect the true blood glucose level.