Translating the A1C Assay Into Estimated Average Glucose Values: Response to Nathan et al.

Nathan et al. (1) present a regression equation that they propose be used to convert measured values of A1C into estimated average glucose (eAG) values, in accordance with recommendations (2) and subject to the condition that their study fulfill its a priori–specified criterion. The criterion declared is that for ≥90% of patients, average glucose values, calculated from continuous glucose monitoring and 7-point glucose measurements over a 3-month span, fall within 15% of the average glucose using the study-wide average glucose as opposed to the A1C regression equation. This criterion was indeed fulfilled (with surprising narrowness: 89.95% of subjects fell within the ±15% limits) (1). Using the proposed equation thus involves an error limit in eAG …