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Energy & Metabolism

HbA1c

HbA1c tells you what your average blood sugar has been over the past 2–3 months — not just where it sat this morning. That makes it far more useful than a one-off fasting test for understanding your risk of diabetes or how well it is being managed. Australian labs print the result in two units (a percentage and a number in mmol/mol) so you may see both on your report; they mean the same thing.

Standard Care
CategoryEnergy & Metabolism
Reference rangeSee your report
Evidence✓Standard Care
Last updated3 July 2026
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Australians live with diabetes (about 1.3 million people), based on 2022–24 national health survey data.

What is hba1c?

HbA1c stands for glycated haemoglobin — haemoglobin with sugar stuck to it. Haemoglobin is the oxygen-carrying protein inside your red blood cells, and when blood glucose stays elevated, glucose gradually coats it in a process called glycation. The HbA1c test measures what percentage of your haemoglobin has been glycated, giving you a picture of your average blood glucose over the preceding 8–12 weeks (roughly 2–3 months). Because red blood cells live for about 3–4 months, HbA1c changes slowly. That means it captures the trend in your glucose control rather than a single moment — useful in a way that a spot glucose reading cannot match. Australian labs report HbA1c in two units side by side: mmol/mol (the IFCC international standard) and % (the older NGSP unit). Both appear on your result and describe the same measurement.

Why is it tested?

HbA1c is used as part of screening for type 2 diabetes and elevated glucose risk, and to track long-term glucose control in people already living with diabetes. Your GP may also order it as routine screening if you have risk factors such as older age, a family history of diabetes, higher body weight, or low physical activity. Unlike a fasting glucose test, HbA1c does not require fasting and is not easily thrown off by a single meal, short-term stress, or the ups and downs of a normal day. One result alone is never enough on its own — your GP reads it alongside your history, symptoms, and any confirmatory testing.

Reference range (Australia)

Normal below 6.0% (below 42 mmol/mol); higher risk 6.0–6.4% (42–47 mmol/mol); diabetes range 6.5% (48 mmol/mol) or above % (and mmol/mol)

No sex-specific variation. Australian guidance (Australian Diabetes Society) uses a higher-risk band of 6.0–6.4% (42–47 mmol/mol) and a diabetes threshold of 6.5% (48 mmol/mol) or above, confirmed on a repeat test in people without symptoms. This is the Australian standard and differs from the US/ADA bands. HbA1c is less reliable where haemoglobin variants, haemolytic anaemia, or significant chronic disease affect red cell turnover. Use the interval printed on your own report.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

A lower-than-range HbA1c is uncommon. It can occur with very well-managed glucose levels, or in people taking diabetes medication where a very low value may mean the dose is doing more than needed. It can also appear with conditions that shorten the lifespan of red blood cells — such as haemolytic anaemia (where red cells break down faster than usual), haemoglobin variants, or kidney disease — because fewer red cells living for their full term means less time for glycation to accumulate, and the HbA1c reads lower than the true glucose level. If you take diabetes medication and your HbA1c is very low, your GP can look at whether the treatment plan needs adjusting.

If your level is in range

An in-range HbA1c (below 6.0%, or below 42 mmol/mol) suggests your average blood glucose over the past 2–3 months has been where it should be — that is genuinely good news. A normal result today does not lock in future risk, though; your GP may suggest rescreening at intervals based on your individual profile, particularly if any of your risk factors change over time.

If your level is high

A higher-than-range HbA1c means your average blood glucose has been elevated over the past 2–3 months. Depending on the level, it can point to a higher risk of developing diabetes, or at higher values suggest that diabetes is likely — but a single result is never enough to make that call. Your GP will arrange a confirmatory test and read your HbA1c alongside your fasting glucose, symptoms, and overall metabolic picture before reaching any conclusion. The reassuring part is that HbA1c is modifiable. Changes to diet, physical activity, and weight can shift it over 2–3 months, and where medication is appropriate your GP will discuss that with you too. Worth raising at your next appointment rather than sitting on.

What can affect your result

HbA1c reflects your average blood glucose over the past 8–12 weeks, so anything that shifts your blood sugar over that time affects the reading. Diet is one of the biggest levers: a pattern high in refined carbohydrates and sugary drinks pushes it up, while regular movement, plenty of wholegrains and vegetables, adequate sleep, and managing stress all support lower levels. Medications matter too. Corticosteroids, certain antipsychotics, and thiazide diuretics (a type of blood pressure tablet) can raise HbA1c; diabetes medicines are designed to lower it. There is also a separate influence that has nothing to do with glucose: conditions that affect red blood cells change how much glycation can accumulate. Anaemia, haemolytic disorders (where red cells break down early), haemoglobin variants, and some chronic illnesses can make HbA1c read higher or lower than the true glucose level. Your GP or pathologist weighs this up when interpreting your result.

When to act

If your HbA1c sits in the higher-risk band (6.0–6.4% / 42–47 mmol/mol), it is worth raising with your GP at your next visit — this points to a higher risk of developing diabetes over time and is not a verdict in itself. If it is in the diabetes range (6.5% / 48 mmol/mol or above), your GP will arrange a confirmatory test before reaching any conclusion and can walk you through what that means for you. Even with a normal result, the habits that keep glucose steady — a whole-food diet, regular movement, enough sleep — are worth keeping up. If you are already being treated for diabetes, HbA1c is usually rechecked every 3–6 months while treatment is being established, then less often once things are stable. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

In Australia a normal HbA1c is below 6.0% (below 42 mmol/mol). A result in the 6.0–6.4% range (42–47 mmol/mol) points to a higher risk of developing diabetes — not a verdict, but a signal to look at lifestyle and recheck. A result of 6.5% (48 mmol/mol) or above is in the diabetes range, and your GP will arrange a repeat test to confirm it first. Australian labs print both units on the same report.

A high HbA1c tells you that your average blood glucose has been elevated over the past 2–3 months. Depending on how elevated it is, that can mean a higher risk of diabetes, or — at 6.5% and above — that diabetes is likely. It does not cause immediate symptoms on its own, and it is one of the more changeable numbers in a blood panel: lifestyle shifts and, where appropriate, medication can bring it down over 8–12 weeks. Your GP confirms the picture before reaching any conclusion and will talk through a plan with you.

A fasting glucose test gives a snapshot — your blood sugar at one moment, after at least 8 hours without eating. HbA1c gives the movie, showing your average glucose over 2–3 months. Because it does not swing with a single meal or a stressful morning, HbA1c is less easily thrown off than a spot reading. Your GP may use both together for a fuller picture, since they answer slightly different questions.

For many people, yes. Diet quality, regular physical activity, weight, sleep, and stress management all influence average blood glucose — and therefore HbA1c. Because the test reflects the full lifespan of your red blood cells, changes take about 8–12 weeks to show up. A GP or accredited practising dietitian can help you shape a plan, and retesting around the three-month mark gives you a clear read on whether things are moving in the right direction.

It depends on your result and your individual risk profile, and your GP is the right person to advise you. As a general guide: if your result is normal and your risk is low, testing every 1–3 years may be enough. In the higher-risk band, annual testing is common. If you are living with diabetes, HbA1c is usually checked every 3–6 months while treatment is being settled, and less often once things are stable.

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