Type 2 Diabetes Mellitus has reached pandemic levels affecting around 10 percent of the population. There is an association with obesity as they share underlying metabolic causes. One of the most popular measures of diabetes is the A1C. It is also called Hemoglobin A1C.


In this article, we will explain how to interpret this important test and also discuss the limitations of it.


Blood sugar (glucose) levels fluctuate widely throughout the day which make it challenging for the physician to know how uncontrolled diabetes is. Hence, there was the need for another test that provides a more consistent measurement about the average blood glucose level.


The A1C provides an idea about the average blood sugar level of over the past 3 months. It is the percentage of glucose attached to the red blood cell.  A normal A1C is less than 5.7%. Between 5.7 to 6.4% is diagnostic for pre-diabetes, while 6.5% and above is indicative of diabetes.


How does it work?


Glucose can attach to proteins via a non-enzymatic process called glycation. There are two types of reactions between glucose and protein.


  • Reversible reaction which leads to the formation of an aldimine
  • Irreversible reaction which leads to the formation of ketoamine.


Hemoglobin formed in new red blood cells enters the circulation with minimal glucose attached. However, red cells are freely permeable to glucose. As a result, glucose becomes irreversibly attached to hemoglobin at a rate dependent upon the amount of glucose concentration in the blood. Approximately 1% of erythrocytes are destroyed every day, while an equal number of new ones are formed. Thus, the average amount of A1C changes in a dynamic way and indicates an approximate average blood glucose concentration over the lifespan of the red cell.


Correlations Between Estimated Average Glucose & A1c:


Glucose (mg/dl) A1c (%)

97 5

126 6

154 7

183 8

212 9

240 10

269 11

298 12


Other medical conditions can affect the accuracy of A1C level. Patients who are being treated with iron/vitamin B12 supplements, presence of liver failure, hemolytic anemia, or bleeding usually have a lower A1c than their glucose level would actually suggest. With increasing patient age, B12 deficiency, or iron deficiency anemia, higher values of A1c are seen for the same glucose level.


Another factor to keep in mind is that the glycation process is irreversible, once  glucose is attached to the hemoglobin molecule in the red blood cells, it stays there for the entire life span of the cells. This means that the A1C will provide you an accurate average of your blood glucose level if your blood sugar level is running very similar level every day. However, if your blood sugar level is running for the past two month between 100-150 and your A1C level is around 5.5 and for one day your blood sugar level is more than 250, this causes glycation of more red blood cells during this day. As a result, these red blood cells will remain glycated for the whole life span of the cells which is around 90 days and your A1C will jump from 5.5 to 6.0 for few weeks while the real changes in the blood sugar was only present for one day.


Bottom line: A1C is a very useful tool in managing diabetes but it has its limitations.


The Metabolism Clinic is established as the destination for weight loss and reversal of diabetes. Based in Charlotte, North Carolina. www.themetabolismclinic.com