The in vivo rate of formation of HbA1c. Autologous RBCs were isolated, labeled with biotin, and then reinfused into study subjects to track RBC survival and glycation over their life span. The HbA1c fraction over time after injection in the whole blood (□) and in the biotinylated RBCs (▿) is shown in 1 subject without (left panel) and 1 with (right panel) DM.