primary care & preventionformula

A1C to Estimated Average Glucose (eAG)

Converts HbA1c to estimated average glucose (eAG) using the ADAG regression equation. This helps patients understand their A1c result in the same units as their daily glucose readings.

inputs

UK labs report in mmol/mol; US labs in %

✓ when to use

Use to translate HbA1c into an estimated average blood glucose for patient-friendly discussion. Helpful for diabetes education, self-management support, and aligning A1c targets with daily glucose monitoring values.

✗ when not to use

eAG is an estimate based on population-level regression, not the individual's actual average glucose. Individual variation in the A1c-glucose relationship exists due to red cell lifespan differences, haemoglobin variants, and other factors. HbA1c is unreliable in haemoglobinopathies (sickle cell, thalassaemia), conditions affecting red cell turnover (haemolysis, transfusion, pregnancy, EPO therapy), and iron deficiency anaemia.

clinical pearls

  • The UK uses mmol/mol (IFCC units) while the US uses % (NGSP/DCCT units). Conversion: IFCC = (NGSP − 2.15) × 10.929. Know which system your patient's lab uses.
  • An HbA1c of 48 mmol/mol (6.5%) corresponds to an eAG of approximately 7.0 mmol/L (126 mg/dL). An HbA1c of 53 mmol/mol (7.0%) corresponds to an eAG of approximately 8.6 mmol/L (154 mg/dL).
  • eAG is a communication tool, not a clinical decision tool. Treatment decisions should be based on A1c (or time-in-range from CGM), not eAG.
  • HbA1c reflects the previous 2–3 months of glucose exposure, weighted toward the most recent 2–4 weeks. A single high-glucose week can disproportionately affect the result.
  • In patients using CGM (continuous glucose monitoring), time-in-range (TIR) and glucose management indicator (GMI) are increasingly replacing A1c as the primary monitoring metric. GMI is derived from CGM data and may differ from lab A1c.

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