What is Hemoglobin, glycated (HbA1c) used for?

Hemoglobin, glycated (HbA1c) (hemoglobin A1c, HbA1c, A1C, or Hb1c; sometimes also HbA1c) is a form of hemoglobin that is measured primarily to identify the average plasma glucose concentration over prolonged periods of time. It is formed in a non-enzymatic glycation pathway by hemoglobin's exposure to plasma glucose. Normal levels of glucose produce a normal amount of glycosolated hemoglobin. As the average amount of plasma glucose increases, the fraction of glycosolated hemoglobin increases in a predictable way. This serves as a marker for average blood glucose levels over the previous months prior to the measurement.
The 2010 American Diabetes Association Standards of Medical Care in Diabetes added the A1c ≥ 48 mmol/mol (≥6.5%) as another criterion for the diagnosis of diabetes.
In diabetes mellitus, higher amounts of glycosolated hemoglobin, indicating poorer control of blood glucose levels, have been associated with cardiovascular disease, nephropathy, and retinopathy. Monitoring the HbA1c in type-1 diabetic patients may improve treatment.
Underlying principle of Hemoglobin, glycated (HbA1c)
In the normal 120-day lifespan of the red blood cell, glucose molecules react with hemoglobin, forming glycosolated hemoglobin. In individuals with poorly controlled diabetes, the quantities of these glycosolated hemoglobins are much higher than in healthy people.
Once a hemoglobin molecule is glycosolated, it remains that way. A buildup of glycosolated hemoglobin within the red cell, therefore, reflects the average level of glucose to which the cell has been exposed during its life-cycle. Measuring glycosolated hemoglobin assesses the effectiveness of therapy by monitoring long-term serum glucose regulation. The HbA1c level is proportional to average blood glucose concentration over the previous four weeks to three months. Some researchers state that the major proportion of its value is related to a rather shorter period of two to four weeks.
The 2010 American Diabetes Association Standards of Medical Care in Diabetes added the A1c ≥ 48 mmol/l (≥6.5%) as another criterion for the diagnosis of diabetes,
Indications and use
Glycosolated hemoglobin testing is recommended for both (a) checking blood sugar control in people who might be pre-diabetic and (b) monitoring blood sugar control in patients with more elevated levels, termed diabetes mellitus. There is a significant proportion of people who are unaware of their elevated HbA1c level before they have blood lab work. For a single blood sample, it provides far more revealing information on glycemic behavior than a fasting blood sugar value. However, fasting blood sugar tests are crucial in making treatment decisions. The American Diabetes Association guidelines are similar to others in advising that the glycosolated hemoglobin test be performed at least two times a year in patients with diabetes that are meeting treatment goals (and that have stable glycemic control) and quarterly in patients with diabetes whose therapy has changed or that are not meeting glycemic goals.
Glycosolated hemoglobin measurement is not appropriate where there has been a change in diet or treatment within 6 weeks. Likewise, the test assumes a normal red blood cell aging process and mix of hemoglobin subtypes (predominantly HbA in normal adults). Hence, people with recent blood loss, hemolytic anemia, or genetic differences in the hemoglobin molecule (hemoglobinopathy) such as sickle-cell disease and other conditions, as well as those that have donated blood recently, are not suitable for this test.
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