A recent consensus statement from an expert panel convened by the American Diabetes Association, European Association for the Study of Diabetes, and the International Diabetes Federation, is now recommending the routine use of A1c for the diagnosis of diabetes, citing it’s superiority to the FPG and 2HPG.
In short, the recommendations are:
A1c >6.5% = diabetes
A1c 6.0 – 6.5% = pre-diabetic state (“at risk for diabetes”)
The statement reviews papers in which the A1c was a better predictor of diabetic complications (retinopathy) than the FPG and 2HPG.
The A1c cannot be relied upon in conditions involving rapid changes in red cell turnover, such as hemolytic anemia, malaria, major blood loss, or recent blood transfusion. Also, since A1c represents chronic glycemic exposure, there are rare clinical instances where the A1c hasn’t “caught up” to the FPG such as rapid onset T1DM or gestational DM.
The ADA has never officially recommended A1c for diabetes diagnosis and has, instead, kept with the FPG and 2HPG for diagnosis. The anticipation is that the ADA, EASD, and IDF will all make official statements soon supporting its use.