Glycated hemoglobin: a long-term blood sugar "monitor" for diabetic patients

Author: Liu Xiangyi, Professor of Beijing Tongren Hospital, Capital Medical University

Reviewer: Wu Xueyan, Chief Physician, Peking Union Medical College Hospital

Glycated hemoglobin is the combination product of hemoglobin and glucose in the blood, and the formation process is slow, continuous and irreversible. Glycated hemoglobin is mainly divided into glycated hemoglobin A1a, glycated hemoglobin A1b, and glycated hemoglobin A1c. Among them, the content of glycated hemoglobin A1c is the most stable, accounting for about 70%, so glycated hemoglobin A1c is usually used as a representative of glycated hemoglobin. Therefore, the level of glycated hemoglobin can reflect the average blood sugar level of an individual in the past 2-3 months, and is unrelated to factors such as the patient's diet, blood drawing time, and insulin injection. It is one of the important indicators for evaluating long-term blood sugar control status. The detection method of glycated hemoglobin (HbA1c) in my country has been basically standardized, and this indicator has been officially included in the diagnostic criteria for diabetes.

It is worth noting that the glycosylated hemoglobin test does not require the patient to be in a fasting state, which makes the test more convenient and flexible, not affected by time and diet, and can provide relatively stable blood sugar control information. Especially for those patients in the intensive care unit who need frequent glucose infusions due to their condition, the glycosylated hemoglobin level will not be affected by short-term blood sugar fluctuations, thus becoming an effective tool for evaluating their long-term blood sugar control.

Despite this, glycated hemoglobin cannot completely replace blood glucose testing. In actual application, fasting blood glucose, 2-hour postprandial blood glucose and oral glucose tolerance test (OGTT) are the main experimental diagnostic indicators for diabetes. On the one hand, there is an essential difference in the detection principles of the two - blood glucose testing reflects the immediate blood glucose level, while glycated hemoglobin reflects the average blood glucose status over a period of time; on the other hand, glycated hemoglobin testing usually requires a specific detection method and requires a purple-capped blood collection tube (the same as a routine blood test), which is different from the sample tube required for conventional blood glucose testing.

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For patients with diabetes, it is crucial to reasonably control the level of glycosylated hemoglobin. Generally speaking, when the glycosylated hemoglobin level is maintained below 7%, it indicates that the patient's blood sugar control is relatively ideal; if the value is between 7%-8%, it means that the blood sugar control effect is poor, and you should consider adjusting the dose of hypoglycemic drugs or improving your lifestyle; and when the glycosylated hemoglobin level exceeds 8%, the patient's risk of diabetes-related complications will increase significantly. It is worth noting that excessive pursuit of too low glycosylated hemoglobin levels (for example, below 6.5%) is not always beneficial, because it may lead to excessive use of hypoglycemic drugs, thereby increasing the risk of hypoglycemia and other adverse reactions. Therefore, in clinical practice, it is usually recommended to set the glycosylated hemoglobin control target at around 7%.

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In addition, considering that glycosylated hemoglobin mainly reflects the long-term trend of blood sugar changes, diabetic patients do not need to perform this test frequently. It is generally recommended to check once every 2-3 months to evaluate the recent blood sugar control status and adjust the treatment plan accordingly.

In addition to glycated hemoglobin, another biomarker related to blood sugar control, glycated albumin, has gradually attracted people's attention in recent years. Glycated albumin refers to a complex formed by the combination of albumin and glucose in plasma. Its metabolic cycle is relatively short, about 2-3 weeks, so it can reflect recent blood sugar fluctuations more quickly. Compared with glycated hemoglobin, glycated albumin shows certain advantages in the early diagnosis of diabetes and the evaluation of treatment effects. However, there is currently no unified standard for the ideal control range of glycated albumin, and its clinical application is not as extensive as glycated hemoglobin.

In the comprehensive management of diabetes, in addition to regular monitoring of blood sugar and glycosylated hemoglobin, it is sometimes necessary to test serum insulin and C-peptide levels. Insulin is a hormone secreted by pancreatic beta cells that is responsible for promoting the utilization and storage of glucose in the body, while C-peptide is a byproduct of the conversion of proinsulin to mature insulin. By analyzing these two indicators, doctors can better understand the state of insulin secretion function in patients, distinguish between type 1 and type 2 diabetes, and guide the selection of personalized treatment strategies.

Finally, for some diabetic patients, especially those with type 1 diabetes, autoantibody testing may be required to assist in diagnosis and assess the risk of disease progression. Common diabetic autoantibodies include anti-islet cell antibodies, insulin autoantibodies, glutamic acid decarboxylase antibodies, and protein tyrosine phosphatase antibodies. The presence of these antibodies often indicates that the patient may have autoimmune-mediated pancreatic β-cell damage, which in turn leads to insulin secretion disorders. Although antibody positivity is not directly equivalent to a confirmed diagnosis of diabetes, it is of great value for early identification, typing, and long-term prognosis assessment of the disease.