Hemoglobin A1c (HbA1c) is the percentage of hemoglobin molecules with attached glucose molecules. HbA1c is an accurate means to estimate the average blood glucose over the preceding 3 months. New hemoglobin molecules have very little attached glucose. Glucose becomes irreversibly attached to hemoglobin in proportion to the concentration of blood glucose. Since 1% of red blood cells are destroyed every day and replaced with an equal number, hemoglobin A1c is a dynamic way of measuring average blood glucose over the life the red blood cell. The average lifespan of red blood cell is 120 days thus hemoglobin A1c provides an accurate estimate of mean blood glucose over the previous 8 to 12 weeks. As such, hemoglobin A1c measurement does not require the person to fast prior to the test.
Normal Ranges for Hemoglobin A1c:
<18 years: Hemoglobin A1c criteria for diagnosing diabetes have not been established for patients who are <18 years of age.
> or =18 years: Increased risk for diabetes (prediabetes): 5.7-6.4%
Diabetes: > or =6.5%
A low HgA1c may indicate that diabetes treatment is too aggressive. In people without diabetes, it is unclear whether a low HgA1c is harmful. Some researchers have found that low HbA1c may be problematic, while others have not. Compared with persons with normal HbA1c, low HbA1c values are associated with an increased risk of and death from various causes in some studies. Low HbA1c values generally reflect a level of chronic low blood sugar or hypoglycemia. There may be an increased risk of liver disease in people with low HbA1c.
An abnormally high level of HgA1c indicates chronic hyperglycemia, or high blood sugar. This is the definition of diabetes mellitus. Hemoglobin A1c is used to diagnose diabetes and track the effectiveness of diabetes treatments. Measurements at or above 6.5% are consistent with a diagnosis of diabetes. In most people with diabetes, the goal of treatment should be to have a hemoglobin A1c level less than 7%.
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