What Your HbA1c Result Really Means (and Why It Matters)

If you have ever had a blood test for diabetes or metabolic health, you have likely encountered HbA1c. It provides a window into your blood sugar control over the preceding two to three months — yet many Australians receive their results without fully understanding the number.

What Is HbA1c?

HbA1c stands for glycated haemoglobin. When glucose circulates in your bloodstream, some attaches to haemoglobin through glycation. Because red blood cells live approximately 120 days, HbA1c reflects your average blood glucose over 2–3 months. In Australia, it is reported as both a percentage and in mmol/mol.

What Do the Numbers Mean?

Normal HbA1c is below 5.7% (< 39 mmol/mol). Prediabetes is 5.7–6.4% (39–47 mmol/mol). Diabetes is diagnosed at 6.5% (≥ 48 mmol/mol) or above on two separate occasions. For people with existing diabetes, the general target is ≤ 7.0% (53 mmol/mol).

HbA1c vs Fasting Glucose

Fasting glucose captures a single point in time and can be affected by what you ate, your stress levels, and sleep quality. HbA1c is not affected by short-term fluctuations and does not require fasting. The RACGP recommends HbA1c as the preferred test for diagnosing type 2 diabetes.

However, HbA1c can be affected by conditions that alter red blood cell turnover — iron deficiency anaemia, thalassaemia, or pregnancy — potentially giving falsely high or low results.

The Prediabetes Opportunity

Diabetes Australia estimates approximately 2 million Australians have prediabetes, and the majority do not know it. The Finnish Diabetes Prevention Study and US Diabetes Prevention Program both showed that modest lifestyle changes — losing 5–7% of body weight and 150 minutes of activity per week — reduced diabetes risk by 58%. Routine HbA1c testing catches this window of opportunity.

Tracking HbA1c Over Time

An HbA1c that has risen from 5.2% to 5.5% to 5.8% over three years is clearly trending in the wrong direction, even though all values are technically non-diabetic. Annual testing allows you to detect these trends early and respond before crossing into the prediabetic or diabetic range.

References

1. RACGP. Management of Type 2 Diabetes: A Handbook for General Practice. East Melbourne: RACGP, 2020.
2. WHO. Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus. Geneva, 2011.
3. Tuomilehto J, et al. Prevention of type 2 diabetes by lifestyle changes. N Engl J Med. 2001;344(18):1343–1350.
4. Diabetes Prevention Program Research Group. Reduction in type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346(6):393–403.