P Mason Explanation of an A1C (clinical laboratory scientist)

 I am a retired Clinical Laboratory Scientist so this is my area of expertise. The a1c is a bit complicated to explain in lay terms but I'll try to simplify it. You've all been told it is a 3 month average of your blood glucose. That's a very general description. The reason is that in most people, red blood cells have an average life span of 3 months. Like hair growth varies from person to person, not everyone's red blood cells live exactly 3 months....that life is influenced by many things, but 3 months is a "ballpark" average. We are constantly producing new red cells, while some have peaked, some are deteriorating, some near death. They're in different stages of life at any given time. So....whereas a normal glucose test measures glucose circulating in the blood in plasma or serum...the liquid part of blood, the a1c uses a completely different methodology to measure just the glucose that attaches & sticks to only the red cells. Bear in mind, that as red cells mature & get near death, they begin to shrink, fragment & break down. They have less surface area for glucose molecules to adhere to. Younger cells, are larger, rounder, & have more surface area for glucose to adhere to so they obviously will have the highest concentrations of glucose. So, since red cells have a life cycle of approximately 3 months, the a1c is measuring the amount of glucose attached to red cells of varying age, size & shape....some have more, others have less. The thing most doctors don't tell you because they may not know, or simply don't take the time to explain, is that since the newest red cells are the biggest, they have the largest concentration of glucose. What's this all mean? Yes, it's about a 3 month average, but the cells that are 4-6 weeks old account for the majority of that average, because they carry the largest amount of glucose due to their size. Basically, since it's an average of all the cells, the newer ones carry more weight. 3 month average yes, but the largest factor of the a1c result is focused on the previous 4-6 weeks. Hope that makes sense. As a side note, people with certain irregularities of their red blood cells such as anemia, & other conditions, may have false low or highs on their a1c results, due to irregularities in number, size or shape of their red cells.