Type 2 Diabetes
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What’s an A1C??
I was just at Dulles airport in DC, flying to the New York area. My gate was
A1C. I realized that people who see A1C may not realize that it also is a
unique blood test that is used to get an approximation of the average blood
glucose over 90 days. How can that be? A single blood sample at a single point
in time can provide that kind of information. Here is how and why it has played
such an important role in diabetes management.
Glucose is a naturally sticky substance from a chemical point of view. In the blood it will stick to red blood cells, proteins, other cells and pretty much any thing with which it comes in contact. As an example, if you took a cup of honey and dipped your hand in it and then walked around your living room touching all of your things, everything would have some honey attached to it. We are only interested in the amount of glucose that sticks to the red blood cell which is directly related to the level of blood glucose at that time.
Secondly, the red blood cell is born, circulates and dies 120 days later. Any time you sample the blood you have a mix of new cells, old cells and in between. A new cell has no glucose, an old cell has more. If the blood glucose has been normal, roughly 5% has stuck to the red blood cells. If the blood glucose is abnormally high for one day that number will not change. If the blood glucose has been high for many days, the A1C will rise. This tells us the level of control and allows us to make changes in medication, diet etc.
Finally the A1C tells us more. It has been shown to correlate for the risk for diabetic complications including cardiovascular but especially the microvascular such as blindness, kidney failure and limb loss. It is important that people with diabetes have an A1C test at regular intervals. Know your number and discuss it with your health care provider.