An adolescent with type 1 diabetes returns for a follow-up visit after his annual check-up last week. You note that his serum glucose is elevated, and his glycosylated hemoglobin (hemoglobin A1C) is 16.7%. This finding suggests poor control of his diabetes over at least which of the following time-periods?

Glucose is nonenzymatically attached to hemoglobin to form glycosylated hemoglobin. The major component of this reaction proceeds very slowly and is irreversible until the hemoglobin is destroyed. The concentration of glycosylated hemoglobin thus reflects glucose concentration over the half-life of the red cell, or about 2 to 3 months. The adolescent in the question may have had poor control of his diabetes for longer than 2 to 3 months, but glycosylated hemoglobin is unable to determine this.