What HbA1c Actually Measures
HbA1c — short for glycated haemoglobin — is a blood test that captures your average blood glucose over the past 8–12 weeks. When glucose circulates in your bloodstream, a small fraction binds permanently to the haemoglobin inside your red blood cells. Because red cells live for around three months, the percentage of glycated haemoglobin gives a long-range view of how high your blood sugar has been running, regardless of what you ate this morning.
That makes HbA1c the most useful single number on your blood test for screening, diagnosing, and monitoring type 2 diabetes — and the reason Diabetes Australia and the RACGP both recommend it as the first-line test for at-risk adults.
How HbA1c Is Reported in Australia
Australian pathology labs report HbA1c in two units side-by-side:
- mmol/mol (millimoles per mole of haemoglobin) — the IFCC standard adopted by Australia in 2011.
- % (percent of haemoglobin that is glycated) — the older NGSP unit, kept for continuity with international research.
The two are mathematically equivalent. A single conversion: HbA1c % = (mmol/mol × 0.0915) + 2.15. So 53 mmol/mol = 7.0%, and 48 mmol/mol = 6.5%. Most Australians find mmol/mol easier to track because the numbers move in larger increments — a 1.0% change is roughly an 11 mmol/mol change.
Normal, Pre-Diabetic and Diabetic Ranges
The thresholds below come from RACGP and Diabetes Australia and apply to non-pregnant adults using a venous blood sample (not finger-prick).
| Category | HbA1c (mmol/mol) | HbA1c (%) |
|---|---|---|
| Normal | <42 | <6.0 |
| Pre-diabetes (high risk) | 42–47 | 6.0–6.4 |
| Diabetes — diagnosis | ≥48 | ≥6.5 |
| Diabetes — typical management target | ≤53 | ≤7.0 |
A single HbA1c of ≥48 mmol/mol is enough to diagnose diabetes in an asymptomatic person, provided the test is performed by an accredited Australian lab (the test must be NATA-accredited and standardised against the IFCC reference method). If the result is borderline, your GP will usually repeat the test on a separate day to confirm before starting treatment.
When You Actually Need an HbA1c Test
Medicare funds one screening HbA1c per asymptomatic adult per year under MBS item 66841, provided you meet at least one risk factor:
- BMI ≥ 30 kg/m² (or ≥ 27 kg/m² for South-East Asian, Indian, Pacific Islander or Aboriginal/Torres Strait Islander people)
- First-degree relative with diabetes
- Previous gestational diabetes
- Polycystic ovary syndrome (PCOS)
- Cardiovascular disease, hypertension, or dyslipidaemia
- Long-term corticosteroid or antipsychotic use
- Aged ≥ 40 with no other risk factors (under the AUSDRISK pathway)
If you already have a diabetes diagnosis, MBS item 66839 funds up to four HbA1c tests per year for monitoring. Most labs bulk-bill both items when a GP referral is on file.
What HbA1c Tells You — and What It Doesn''t
HbA1c is excellent for screening and long-term monitoring but has some real limitations:
- It misses post-meal glucose spikes. Two people with the same HbA1c can have very different post-prandial patterns. If you experience symptoms after meals (sweating, fatigue, dizziness), ask about a continuous glucose monitor (CGM) or a glucose tolerance test.
- It cannot diagnose type 1 diabetes reliably. Type 1 onset is rapid; HbA1c lags behind. A fasting glucose, ketone test, and antibody panel are usually more informative.
- It is not used in pregnancy after the first trimester. The reference ranges shift, and gestational diabetes is screened with the oral glucose tolerance test (OGTT) at 24–28 weeks.
- It can be misleading in the first 8 weeks of any major change — a new medication, a 5 kg weight loss, or a pregnancy will not yet be reflected. Wait at least 12 weeks before judging the impact.
What Can Make HbA1c Inaccurate
Anything that shortens or lengthens red cell lifespan changes the result. The most common Australian causes of an inaccurate HbA1c are:
- Iron deficiency anaemia — falsely raises HbA1c. Treating the anaemia usually drops HbA1c by 5–10 mmol/mol within 3 months.
- Recent blood transfusion (within 3 months) — falsely lowers HbA1c.
- Haemoglobinopathies — sickle cell trait, beta-thalassaemia minor, and HbE variants are more common in people of Mediterranean, African, and South-East Asian background. Some pathology methods are unaffected; others give unreliable readings. NSW Health Pathology and Sullivan Nicolaides flag affected results automatically.
- Chronic kidney disease (eGFR < 30) — falsely lowers HbA1c due to reduced red cell survival.
- Recent severe blood loss or haemolysis — falsely lowers HbA1c.
If your HbA1c does not match your symptoms or your home glucose readings, your GP can confirm with a fasting glucose, an OGTT, or a fructosamine test (which captures only the past 2–3 weeks).
What to Do With a High or Borderline Result
If your HbA1c sits in the pre-diabetes range (42–47 mmol/mol), treat it as a warning, not a diagnosis. Around 30% of Australians with pre-diabetes progress to type 2 diabetes within five years if they do nothing — but the same data shows that structured lifestyle changes can cut that risk by more than half:
- Lose 5–10% of body weight if you''re overweight — this is the single biggest lever.
- Walk 30 minutes most days, ideally after meals, to blunt post-prandial glucose spikes.
- Resistance train twice a week — muscle is the main glucose sink.
- Swap refined carbohydrates for whole foods, especially at breakfast (the highest-glucose meal for most people).
- Aim for 7–9 hours of sleep; sleep restriction directly worsens insulin sensitivity.
If your HbA1c is in the diabetes range (≥48 mmol/mol), your GP will likely refer you for a HbA1c repeat plus fasting lipids, kidney function (eGFR + ACR), liver function, and a foot/eye check. Treatment is individualised — many people achieve target ranges with lifestyle changes alone, others need metformin first-line, and some use newer agents (SGLT2 inhibitors, GLP-1 receptor agonists) that are now PBS-funded for high-risk adults.
Tracking HbA1c Over Time
The single most useful thing you can do with an HbA1c result is graph it. A snapshot can be misleading — a 5 mmol/mol jump might look alarming on its own, but trivial when you see your last six results in context. Most Australian pathology portals (My Health Record, Sonic Healthcare''s Sonic DX, Healius MyResults) show only your most recent few values. Uploading every PDF you receive to a tracker like BloodTrack gives you the full multi-year trend, side by side with related markers — fasting glucose, lipids, kidney function, liver function — that all move together when you change diet, exercise, or medication.
For people on TRT or with PCOS, HbA1c is especially worth tracking quarterly. Both groups have higher background risk of insulin resistance, and both benefit disproportionately from catching changes early.
Bottom Line
HbA1c is one of the most useful single numbers on your blood test, but only if you understand the units, the thresholds, and the situations where it can mislead. Test annually if you have any risk factor (Medicare covers it), retest every 3 months if you have diabetes, and always interpret a single result against your trend rather than in isolation.