Hemoglobin A1c (HbA1c)

When glucose circulates in your blood, a fraction of it sticks irreversibly to haemoglobin inside red blood cells — that's HbA1c. Because red blood cells live ~120 days, the HbA1c reading reflects average blood sugar across the previous 2–3 months and is much harder to game than a single fasting glucose. It is the WHO- and ADA-endorsed test for diagnosing and monitoring type 2 diabetes.

• Normal: below 5.7% (below 39 mmol/mol).
• Prediabetes: 5.7-6.4% (39-46 mmol/mol).
• Diabetes: 6.5% or above (48 mmol/mol or above), confirmed on repeat.
• Anaemia, recent blood loss and some haemoglobin variants can distort HbA1c.

Your lab's printed range is what counts.

• 5.7–6.4% — prediabetes (impaired fasting glucose). Lifestyle intervention reduces progression risk by 40–60%.
• ≥6.5% — meets diabetes diagnostic threshold on confirmation.
• >9% — poorly controlled diabetes; raises retinopathy, nephropathy and cardiovascular risk significantly.
• >10% — endocrinology referral recommended.

• Recent significant blood loss — replaces older glycated red cells with fresh ones.
• Hemolytic anaemia — shortened red-cell lifespan reduces glycation window.
• Recent transfusion — donor cells lower the average.
• Hemoglobinopathies (sickle cell trait, thalassaemia) — some lab methods over- or under-read.

• HbA1c itself is silent - it is an average, and early prediabetes usually causes no symptoms at all.
• When glucose is high enough to cause symptoms, they include thirst, frequent urination, fatigue and blurred vision.
• Because it can be symptom-free, HbA1c is valued as a screening and monitoring number.