For the glycosylated hemoglobin "HbA1c", everyone is familiar with it. The China Type 2 Diabetes Prevention and Treatment Guidelines once again make it shine and give it a new mission as a new standard for Chinese diabetes diagnosis. Today, we're going to talk in more detail about glycosylated hemoglobin.
What is an indicator of glycosylated hemoglobin?
Glycosylated hemoglobin (HbA1c) is the product of a slow, continuous, non-enzymatic binding of hemoglobin to glucose in red blood cells, and this binding is irreversible. The percentage of hemoglobin in the blood that binds to glucose as a percentage of the total hemoglobin is measured, and its normal reference range is 4% to 6%.
Since the lifespan of red blood cells is 120 days, glycosylated hemoglobin can indirectly reflect the average blood glucose level of patients in the past three months.
Are you aware of these 4 clinical effects?
Glycosylated hemoglobin (HbA1c) has good stability, is not affected by occasional blood glucose increase or decrease, can objectively reflect the average blood glucose level of diabetic patients in the past 2 to 3 months, and it is closely related to diabetic complications, especially microangiopathy, and has important clinical value in the clinical diagnosis and monitoring of diabetes.
It is used to assess the overall control of blood glucose in patients over the last 2 to 3 months
Glycosylated hemoglobin can accurately reflect the degree of long-term blood glucose control and plays an important role in blood glucose monitoring. It can be said that no other blood glucose control indicator "includes fasting blood glucose, post-stress blood glucose, blood glucose fluctuations, etc." as stable as glycosylated hemoglobin, so all the authoritative guidelines for diabetes regard glycosylated hemoglobin as the gold standard for blood glucose control in diabetic patients.
Used to predict the risk of chronic complications of diabetes
HbA1c levels are closely related to the occurrence of chronic complications of diabetes , particularly microvascular complications , and can be used as an important indicator of chronic complications. The observations found that when HbA1c < 7%, the risk of chronic complications of diabetes was small, and once HbA1c > 7%, the risk of chronic complications was significantly increased.
The UK prospective diabetes study "UKPDS" demonstrated that the higher HbA1c, the greater the risk of various complications of diabetes in patients, and every 1% decrease in HbA1c reduced diabetic microangiopathy by 37%, peripheral vascular disease by 43%, myocardial infarction by 16%, stroke by 12%, and the risk of diabetes-related death by 21%.
In addition, many large-scale clinical studies at home and abroad "DCCT, UKPDS, etc.", have confirmed that the higher HbA1c, the greater the risk of various complications of diabetes in patients, and reducing HbA1c can significantly reduce the occurrence of various chronic complications of diabetes.
As a diagnostic indicator of diabetes
Compared with the transient indicator of spot blood glucose, glycosylated hemoglobin is a stable indicator of long-term (2 to 3 months) blood glucose levels, more in line with the definition of diabetes, and can better reflect long-term blood glucose levels and the risk of chronic complications.
In 2010, the American Diabetes Association's ADA diabetes management guidelines have made glycosylated hemoglobin ≥ 6.5% as one of the diagnostic criteria for diabetes. In 2011, the World Health Organization "WHO" also recommended that all these points of glycosylated hemoglobin be used in countries and regions where conditions permit to diagnose diabetes.
Previously, due to the standardization of the detection method of glycosylated hemoglobin in various regions of the mainland, the instruments and quality control for the determination of glycosylated hemoglobin could not meet the standard requirements, and at the same time, there was a lack of big data on the normal value of glycosylated hemoglobin in China, so the glycosylated hemoglobin was not used as the diagnostic standard for diabetes in China.
Now that all this has changed completely, the time is ripe for glycosylated hemoglobin as the diagnostic criterion for diabetes. At the 24th National Academic Conference of the Diabetes Branch of the Chinese Medical Association, it was officially announced that glycosylated hemoglobin would be used as the diagnostic criterion for diabetes.
For differential diagnosis of "stress hyperglycemia"
Various stresses such as myocardial infarction and cerebrovascular accidents can cause a temporary increase in blood glucose, but HbA1c is not necessarily elevated in patients, and HbA1c is also elevated if the patient is diabetic. The identification of the two has some value in guiding treatment and judging prognosis.
Advantages of glycosylated hemoglobin compared to blood glucose monitoring
The difference between blood glucose and glycosylated hemoglobin
Image source: The author draws
Usually, the trend of glycosylated hemoglobin and blood glucose is consistent, that is, the higher the blood glucose, the higher the glycosylated hemoglobin, but there are exceptions, and sometimes the two changes are not consistent, which will be discussed in the subsequent limitations on glycosylated hemoglobin.
Which factors affect the test results of HbA1c
In addition to being closely related to the "blood glucose concentration", the level of glycosylated hemoglobin is also affected by various factors such as the lifespan of red blood cells and the contact time between blood glucose and hemoglobin.
Any factor that prolongs the lifespan of red blood cells or increases the exposure of red blood cells to high sugar environments can cause increased HbA1c, and iron deficiency anemia is the more common factor causing increased HbA1c;
Any factor that can shorten the lifespan of red blood cells or reduce the exposure time of red blood cells to high-sugar environments can cause a decrease in HbA1c, such as hemolytic anemia, cirrhosis and hypersplenism, patients receiving blood transfusion therapy, and EPO treatment in patients with diabetic nephropathy, etc. Because the patient's red blood cell lifespan is shortened, the glycosylated hemoglobin measurement results are often low.
In addition, because the formation of glycosylated hemoglobin is a slow process, for some rapidly progressive type 1 diabetes "such as "fulminant type 1 diabetes", glycosylated hemoglobin may not be able to catch up with the speed of acute blood glucose changes, HbA1c test results are often normal or only mildly elevated, can not truly reflect the rapid increase in blood glucose levels, in this case, should be based on the patient's blood glucose test results at that time.
HbA1c controls in what range is good
It is generally believed that glycosylated hemoglobin in 4% to 6% indicates that blood glucose control is normal; 6% to 7% indicates that blood glucose control is ideal; 7% to 8% indicates that blood glucose control is general; 8% to 9% indicates that control is not ideal, and it is necessary to strengthen blood glucose control, pay more attention to diet structure and exercise, and adjust the treatment plan under the guidance of doctors; >9% indicate that blood glucose control is very poor, which is a risk factor for the development of chronic complications.
Most diabetic patients have glycemic control goals for HbA1c<7%, but for each individual, HbA1c control goals are different.
HbA1c <7%: Suitable for most adults with type 2 diabetes (except pregnant women).
HbA1c < 6.5%: Suitable for young, uncomplicated, long-lived type 2 diabetics.
HbA1c < 8.0%: Suitable for patients with a history of severe hypoglycemia, short life expectancy, significant microvascular or macrovascular complications, or severe comorbidities and a longer course of diabetes.
BS+HbA1c+TIR
Earlier we talked about the advantages of glycosylated hemoglobin, but it also has its own shortcomings:
1. It cannot reflect the patient's daily blood glucose fluctuations. Even if HbA1c levels are exactly the same, there are still large differences in blood glucose fluctuations between patients, and this difference can lead to different clinical outcomes, and the greater the blood glucose fluctuations, the worse the prognosis of the patient.
2. It cannot be used as a basis for adjusting the medication. The adjustment of insulin dose must rely on real-time monitoring of fasting blood glucose and postprandial blood glucose values, otherwise serious consequences such as high or low blood sugar will occur.
Therefore, although glycosylated hemoglobin is the gold standard for blood glucose control, it is not yet a complete substitute for transient blood glucose measurement.
The latest 2020 edition of the "China Type 2 Diabetes Prevention and Control Guidelines" recommends time in range (TIR) as an important indicator of glucose monitoring and control, TIR represents the time ratio of glucose in the target range (usually 3.9 to 10.0mmol/L) within 24 hours, which can better reflect the degree of short-term blood glucose variation and effectively compensate for the lack of HbA1c.
The organic combination of blood glucose, HbA1c and TIR is an ideal blood glucose monitoring mode, which can more comprehensively reflect the true situation of patient blood glucose control and provide sufficient decision-making basis for refined adjustment of treatment plans.
Source: Lilac Garden Endocrine Time
Edited by: Yeah Reviewer: Xiao Ran