Translating the A1C assay into estimated average glucose values: response to Nathan et al. - Rodríguez-Segade S; Rodríguez J; Paz JM; Camiña F; Leslie RDG; Kilpatrick ES; Nathan DM; Rodríguez-Segade, Santiago; Rodríguez, Javier; Paz, Juan Manuel; Camiña, Felix (Diabetes Care, 2009)