Glycosylated Hemoglobin

Glycosylated hemoglobin is formed by a nearly irreversible reaction in which glucose becomes linked with hemoglobin. Glycosylated hemoglobin, hemoglobin A₁, hemoglobin A_1C, and fast hemoglobin all refer to this posttranslational modification of hemoglobin by the addition of a glucose moiety. The proportion of hemoglobin that is glycosylated is dependent primarily on the age of the RBC and the quantity of glucose to which it is exposed. Once formed, glycosylated hemoglobin remains in the erythrocyte for the duration of its life span. Assuming that RBC survival is 120 days, about 6% to 8% of hemoglobin is glycosylated in normoglycemic individuals, and 10% to 17% or more of hemoglobin will exist in the glycosylated form in hyperglycemic subjects. The glycosylation process is so slow that glycosylated hemoglobin measurements do not vary with minute-to-minute changes in blood glucose concentrations, but are believed to reflect a composite of all glucose levels that