Which of the following hemoglobins has glucose-6-phosphate on the amino-terminal valine of the beta chain?

• A. S
• B. C
• C. A2
• D. A1c

Answer: (D)

Glycation of hemoglobin is used clinically to assess long-term blood glucose. This occurs when glucose nonenzymatically attaches to the N-terminal valine of the beta chain, forming HbA1c. Among the options, HbA1c is the one that represents this glycated form of hemoglobin and is routinely measured to monitor glucose control over the past 2–3 months.

The other hemoglobins are not glycated forms: HbS carries a mutation in the beta chain (glutamic acid replaced by valine at position 6), HbC has a different substitution at the same position, and HbA2 is a different hemoglobin composed of alpha and delta chains. None of these involve the N-terminal beta-chain glycation that defines HbA1c.