1About HbA1c — Interpretation & Diabetes Targets
HbA1c (Glycated Haemoglobin) reflects average plasma glucose over the preceding 2–3 months (the average erythrocyte lifespan) and represents the gold standard metric for chronic glycaemic monitoring. It is expressed as a percentage (NGSP/DCCT standard) or in mmol/mol (IFCC international standard).
Diagnostic thresholds per ADA 2024 and RSSDI India guidelines:
- Normal: < 5.7% (< 39 mmol/mol)
- Prediabetes: 5.7% – 6.4% (39 – 47 mmol/mol)
- Diabetes Mellitus: ≥ 6.5% (≥ 48 mmol/mol) confirmed on two occasions
When is HbA1c unreliable? Red cell lifespan alterations cause substantial discordance. Conditions that falsely decrease HbA1c include haemolytic anaemia, hemoglobinopathies (HbS, HbE, HbC, thalassaemia variants), acute blood loss, and recent transfusion. Conversely, iron-deficiency anaemia and severe renal impairment with carbamylated haemoglobin spuriously elevate reported HbA1c. In such settings, fructosamine or glycated albumin should be utilized.
2HbA1c & eAG Reference Conversion Table
| DCCT (%) | IFCC (mmol/mol) | eAG (mg/dL) | eAG (mmol/L) | Clinical Category |
|---|