HbA1c (glycated haemoglobin) reflects the average plasma glucose over the preceding 8-12 weeks. Each 1% rise in HbA1c corresponds to roughly a 28.7 mg/dL rise in average glucose (Nathan, ADAG study 2008).

eAG (estimated Average Glucose) converts the percentage into a glucose number patients can relate to from their glucometer. Formula: eAG (mg/dL) = 28.7 × HbA1c − 46.7.

• Normal: HbA1c <5.7% (<39 mmol/mol)
• Prediabetes: HbA1c 5.7-6.4% (39-46 mmol/mol)
• Diabetes: HbA1c ≥6.5% (≥48 mmol/mol) — confirm with repeat test unless symptomatic with random glucose ≥200 mg/dL
• ICMR/RSSDI add-on: Asian-Indians have higher CV risk at lower BMI — screen from BMI ≥23 kg/m², age ≥35, or any risk factor

• Most non-pregnant adults: <7.0% (ADA, ICMR, RSSDI)
• Young, newly diagnosed, low hypoglycaemia risk: <6.5%
• Elderly, frail, high hypoglycaemia risk, advanced complications: 7.5-8.0% acceptable
• Pregnancy / GDM: <6.0% if achievable without hypoglycaemia (FOGSI)

• Haemoglobinopathies — HbS, HbE, HbC, beta-thalassaemia trait (common in eastern India, NE states)
• Anaemia — iron deficiency falsely raises HbA1c; haemolysis falsely lowers
• Recent blood transfusion / EPO therapy
• Advanced CKD (stage 4-5) — shortened RBC lifespan
• Pregnancy — use OGTT (FOGSI/DIPSI single-step test)
• Alternative: fructosamine (3-week window) or continuous glucose monitoring (TIR)