How Quickly A1c moves after a change in Sugar Average
A1c versus time after a sudden change in the 24 hour average BG
Most diabetes sources will say that an A1c represents your average sugar over a three month period. That was a conjecture that was so often seen it was taken by most to be a proven fact. The conjecture was based on an assumption that a change in an A1c was directly linked to the half life of red blood cells. What was wrong was the assumption that the red cells had to die and be replaced for the glycation percentage in a group of such cells to change.
In an arcane article, a chemist derived the forward and reverse reaction dynamics equations that describe the time related behavior of glycation formation and dissolution when average sugar level rises or drops, respectively. They were what is called in calculus, simultaneous linear partial differential equations. Another group, seeing them, but having no closed form solution for them, put them into a computer model they wrote. It was a model that could produce A1c vs time prediction graphs from a daily average BG vs time input. Armed with their computer predictions, they did an in-hospital validation of their model with volunteers and found it was correct.
Upon seeing one of the test case A1c graphs they got from their computer modeling of a step change in the input, it was realized that there was a simple equation, that of an asymptotic exponential rise, that would produce virtually the same result. It was not necessary to use their computer model to examine the behavior of A1c after a simple step change in the daily average sugar level takes place.
If the 24 hour average of sugar level suddenly changes, as it may when a person changes his BG control strategy suddenly, A1c does not instantly jump to a new value. Rather, it continuously changes for about 50 days. During the 50 days the A1c moves toward that new end point but it will have intermediate values between the starting A1c and the day 50 new value during that time.
The below files has a graph that shows how, day by day, an A1c responding to a sudden step change in daily average sugar level, reaches a new value. You can look at that and decide when it makes sense to have a new A1c test performed after you cause your daily average sugar value to change.
A1c_VS_T.XLS (Microsoft Excel)
A1c_VS_T.QPW (Quatro Pro)
A1c_VD_.ODS (Open Office)
A1C_VS_T.ODS (Open Office)
Questions? Contact R. Sebol at the DSM-L list. If you are a current member, you can post to the list by clicking here.