How the HbA1c conversion is calculated
HbA1c can be reported as an NGSP percentage (US/older standard) or an IFCC value in mmol/mol (SI/international standard). Estimated average glucose (eAG) translates the result into the same units as a glucometer.
Normal values & diagnostic thresholds
| HbA1c (NGSP %) | Category |
|---|---|
| < 5.7% | Normal |
| 5.7 – 6.4% | Prediabetes |
| ≥ 6.5% | Diabetes |
| < 7.0% (typical target) | Reasonable control in known diabetes |
Clinical use
HbA1c reflects average blood glucose over the preceding ~2–3 months (the lifespan of a red blood cell) and is used both to diagnose diabetes and to monitor long-term glycaemic control. A single ≥6.5% result should generally be confirmed with a repeat test unless the patient has unambiguous hyperglycaemic symptoms. HbA1c can be unreliable in conditions that affect red cell turnover — haemolytic anaemia, recent transfusion, chronic kidney disease, pregnancy, and haemoglobinopathies — where fasting/random glucose or an oral glucose tolerance test is preferred.
Frequently asked questions
What is HbA1c?
HbA1c (glycated haemoglobin) reflects average blood glucose over roughly the past 2–3 months, based on how much glucose has attached to red blood cells during their lifespan. It's used both to diagnose diabetes and monitor long-term control.
What HbA1c level indicates diabetes?
6.5% (48 mmol/mol) or higher is diagnostic of diabetes per ADA criteria, usually confirmed with a repeat test unless symptoms are unambiguous. 5.7–6.4% is classified as prediabetes.
What is a good HbA1c target for someone with diabetes?
A common general target is below 7% for many adults with diabetes, though targets are individualised — tighter for younger, otherwise-healthy patients, and more relaxed for older patients or those with significant comorbidities or hypoglycaemia risk.
How often should HbA1c be tested?
Typically every 3–6 months in people with diabetes, depending on how stable control is and whether treatment has recently changed; less frequently once well-controlled and stable.
References
- American Diabetes Association. Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1).
- Nathan DM, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31:1473–1478.
- NGSP / IFCC HbA1c harmonisation. ngsp.org