Key Takeaways
- HbA1c reflects your average blood glucose over the past 2–3 months, not just one moment in time
- A result of 48 mmol/mol (6.5%) or above is used to diagnose type 2 diabetes in Australia
- The ADA recommends most adults with diabetes aim for an HbA1c below 53 mmol/mol (7%)
- Targets are individual — your doctor will set a goal based on your age, medications and health history
- Small reductions in HbA1c meaningfully lower the risk of long-term diabetes complications
If you have diabetes or pre-diabetes, your doctor will regularly order an HbA1c test — sometimes called an A1C or glycated haemoglobin test. It is one of the most important measurements in diabetes management, yet many people are unsure what it actually measures, what the numbers mean, and what a "good" result looks like for their situation.
This guide explains everything you need to know about HbA1c in plain English, including how the test works, how to interpret your result, and practical steps that may help improve your numbers over time.
What Does HbA1c Actually Measure?
Haemoglobin is a protein inside your red blood cells that carries oxygen around your body. When glucose (sugar) is present in your bloodstream, some of it naturally attaches to haemoglobin — a process called glycation. The more glucose in your blood over time, the more haemoglobin becomes glycated.
Because red blood cells live for approximately 2–3 months before being replaced, measuring the proportion of glycated haemoglobin (HbA1c) gives a picture of your average blood glucose levels over that entire period. This is very different from a fingerprick or continuous glucose monitor (CGM) reading, which only reflects your blood sugar at a single moment.
Think of it this way: a fingerprick reading is like a photograph, while HbA1c is like a short film of the past three months.
Why 2–3 months?
Red blood cells are continuously being produced and dying off over roughly a 90-day cycle. Because the HbA1c test measures glucose attached to haemoglobin across all the red blood cells in your body at the time of testing, it naturally reflects an average weighted towards more recent weeks — but still captures the full 2–3 month window.
How to Read Your HbA1c Result
In Australia, HbA1c results are reported in mmol/mol (millimoles per mole). In the United States, results are reported as a percentage (%). Both formats appear in research and on product information, so it helps to understand both.
| HbA1c (mmol/mol) | HbA1c (%) | What it generally indicates |
|---|---|---|
| Below 39 | Below 5.7% | Normal range — no diabetes |
| 39–47 | 5.7–6.4% | Pre-diabetes range |
| 48 or above | 6.5% or above | Diabetes diagnostic threshold |
| 53 or below | 7% or below | General target for most adults with diabetes (ADA) |
| 64 or below | 8% or below | Target for some older adults or those at hypoglycaemia risk |
These thresholds are guidelines used across Australia, the UK and internationally. Your own doctor may set a personalised target that differs from the general recommendations, based on your age, how long you have had diabetes, your medications, and other health factors.
HbA1c Targets: One Size Does Not Fit All
The most commonly cited target — HbA1c below 53 mmol/mol (7%) — comes from major guidelines including those of the American Diabetes Association (ADA) and Diabetes Australia. However, this is a population-level guideline, not a universal rule.
For some people, a lower target (e.g. below 48 mmol/mol / 6.5%) may be appropriate, particularly for younger people with recently diagnosed type 2 diabetes who are managing well with lifestyle changes alone.
For others, a higher target may be appropriate — for example:
- Older adults, where strict control may increase the risk of dangerous hypoglycaemia (low blood sugar)
- People with significant other health conditions or limited life expectancy
- Those who experience frequent hypoglycaemia at lower HbA1c levels
- People with type 1 diabetes who are using insulin and need flexibility
This is why it is important to discuss your personal HbA1c target directly with your GP or endocrinologist rather than comparing your result to someone else's goal.
Why Does HbA1c Matter? The Link to Complications
Long-term elevated blood glucose damages blood vessels and nerves throughout the body. The HbA1c test is used to track this risk because it reflects prolonged exposure to high glucose, which is what causes the most harm.
Large clinical trials — particularly the landmark UKPDS (UK Prospective Diabetes Study) and the DCCT (Diabetes Control and Complications Trial) — established that reducing HbA1c is directly linked to lower rates of:
- Diabetic eye disease (retinopathy) — a leading cause of vision loss
- Kidney disease (nephropathy) — which can progress to kidney failure
- Nerve damage (neuropathy) — causing pain, numbness and foot complications
- Cardiovascular disease — heart attack and stroke
Even modest reductions in HbA1c — for example, dropping from 64 to 53 mmol/mol (8% to 7%) — are associated with meaningful reductions in risk. This is why even gradual improvement matters.
A 1% reduction matters more than you might think
Research from the UKPDS found that each 1 percentage point reduction in HbA1c (e.g. from 8% to 7%) was associated with approximately a 37% reduction in the risk of microvascular complications and a 14% reduction in heart attack risk. Small changes accumulate into large long-term benefits.
What Can Affect Your HbA1c Result?
While HbA1c is a reliable and widely used test, certain conditions can affect the result and make it less accurate. Your doctor should be aware of these if they apply to you:
Conditions that may falsely lower HbA1c
- Iron deficiency anaemia (before treatment)
- Haemolytic anaemia (where red blood cells are destroyed faster than normal)
- Recent blood transfusion
- Pregnancy (particularly the second and third trimesters)
- Some haemoglobin variants (e.g. haemoglobin S in sickle cell trait)
Conditions that may falsely raise HbA1c
- Iron deficiency anaemia (before treatment begins)
- Vitamin B12 or folate deficiency
- Chronic kidney disease
- High doses of aspirin or some other medications
If you have any of these conditions, your doctor may rely more on other measures such as fructosamine testing or continuous glucose monitoring (CGM) data to assess your glucose control.
How Often Should You Have an HbA1c Test?
For most people with diabetes in Australia, Diabetes Australia recommends:
- Every 3 months if your HbA1c is above your target or if your treatment has recently changed
- Every 6 months if your HbA1c is stable and at or near your target
For people with pre-diabetes (HbA1c 39–47 mmol/mol), testing every 6–12 months is generally recommended to monitor whether levels are progressing, stable or improving.
Using the DiabetesHub A1C Calculator
Our free A1C Estimator tool allows you to convert between HbA1c percentage and mmol/mol, and also calculates your estimated average glucose (eAG) — a figure that represents what your daily blood sugar readings would need to average to produce a given HbA1c result. This can help make the number feel more tangible and relevant to your day-to-day management.
Important: This article is for information only
HbA1c results should always be interpreted by a qualified healthcare professional in the context of your individual health history, medications and circumstances. Do not change your treatment or medication based on information in this article. Always speak with your GP or endocrinologist about what your result means for you personally.
Summary
The HbA1c test is one of the most valuable tools available for understanding and managing diabetes over the long term. It provides a view of average blood glucose over 2–3 months that a single fingerprick cannot offer, and it is directly linked to the risk of developing serious diabetes complications. Understanding what your result means — and working with your healthcare team to set and pursue a personalised target — is a key part of living well with diabetes.