Glycated haemoglobin (HbA1c) is a measurement made on which component of blood?

Correct answer: C. Red blood cells (haemoglobin within erythrocytes)

• A. Leukocytes have no role in this assay.
• B. Glycated plasma PROTEINS are measured as fructosamine, which reflects only the previous 2–3 weeks and is a different test — useful precisely when HbA1c is unreliable.
• C. CORRECT. HbA1c measures the fraction of HAEMOGLOBIN inside RED BLOOD CELLS that has been non-enzymatically glycated. Because the erythrocyte lifespan is roughly 120 days, the result reflects average glycaemia over the preceding 2–3 months and cannot be manipulated by fasting or by a single good day.
• D. Serum glucose gives an instantaneous value only; it is the fasting or random glucose test, not HbA1c.

Note: Interpretation: below 5.7% normal, 5.7–6.4% prediabetes, 6.5% or above diabetic, and above 7% generally regarded as poorly controlled for dental purposes. Any condition that shortens red-cell survival — haemolysis, recent transfusion, sickle cell disease, pregnancy — makes HbA1c falsely LOW; use fructosamine instead.