This article published today in the Journal of Diabetes and Its Complications proposes a novel and useful way to assess the time-averaged A1C of a population. In the DCCT/EDIC clinical trial, which still provides the best data on long-term complications and A1C control, it was the time-averaged A1C that most closely correlated with complications. In many populations of interest today, a time-averaged A1C is not available; for instance in populations covered by a health insurance payor. This report shows that a graph of retinopathy development against years of diabetes produces a very tight linear trend line (r=0.99), and they argue that the slope of this line correlates with the time-averaged A1C of the population. I think that there are a number of populations in which this approach would add useful information not otherwise available.
See abstract here.