HbA1c (glycated haemoglobin) measures the average blood glucose level over the past 2–3 months. It reflects how much glucose has attached to haemoglobin in red blood cells. In Australia it is reported in mmol/mol. It is used to diagnose and monitor diabetes.

Do I need to fast before an HbA1c test?

No. HbA1c reflects a 2–3 month average and is not affected by what you ate that day. No fasting is required. It can be tested at any time of day.

What is the difference between HbA1c and blood glucose?

A blood glucose test (fasting or random) gives a snapshot of your glucose level at one moment. HbA1c gives a 2–3 month average. Both are used in diabetes diagnosis and management but provide different information. HbA1c is more convenient as it doesn't require fasting.

What units is HbA1c reported in Australia?

In Australia, HbA1c is reported in mmol/mol (the IFCC unit). Older Australian reports and US guidelines use % (NGSP unit). Both measure the same thing — use the HbA1c Converter to convert between them.

What Is HbA1c? — Blood Sugar Average Test Explained

What HbA1c measures

HbA1c (haemoglobin A1c, or glycated haemoglobin) measures the average blood glucose level over the past 2–3 months. It reflects how much glucose has become attached to haemoglobin — the protein inside red blood cells that carries oxygen.

Because red blood cells live for approximately 3 months, HbA1c captures a rolling average of blood glucose over that time. Unlike a fasting glucose or random glucose test — which gives a snapshot of one moment — HbA1c gives a longer-term picture.

In Australia, HbA1c is reported in mmol/mol (millimoles per mole). Older reports and international guidelines sometimes use % — the two can be converted.

Why your GP ordered it

HbA1c is ordered to:

Diagnose type 2 diabetes and pre-diabetes (impaired glucose regulation)
Monitor blood glucose control in people already diagnosed with diabetes — typically every 3–6 months
Assess cardiovascular risk in people with metabolic syndrome or obesity
Screen for undiagnosed diabetes in people at risk — those with obesity, family history, gestational diabetes history, or polycystic ovary syndrome (PCOS)
Adjust diabetes medications or insulin doses based on long-term control

HbA1c is not used alone to diagnose or exclude diabetes in people with conditions affecting red blood cell turnover — including haemolytic anaemia, iron deficiency, blood transfusions, or certain haemoglobin variants. Your GP will choose the most appropriate test for your situation.

What the test involves

HbA1c is a blood test that does not require fasting. It can be done at any time of day, which makes it a convenient alternative to fasting glucose testing.

📋 Source: RCPA Pathology Manual — HbA1c. Australian Diabetes Society — HbA1c diagnosis and targets. IFCC/NGSP unit conversion. Diabetes Australia. rcpa.edu.au
Your doctor or healthcare provider knows your history and circumstances — always follow their personalised advice over general information.

The test is a standard blood draw. Results are usually available within 24 hours. Unlike blood glucose monitors used at home, the laboratory HbA1c test does not vary based on what you ate that morning.

Australian laboratory context

In Australia, HbA1c is reported in mmol/mol (the IFCC unit), which replaced the older % (NGSP/DCCT) unit in 2013. Both units still appear on some reports and guidelines. The two can be converted — see the HbA1c Converter below.

The Australian Diabetes Society diagnostic thresholds for HbA1c are consistent with World Health Organization guidance. Diagnosis requires two separate abnormal results on different occasions unless symptoms are present, or a single unequivocal result with symptoms.

HbA1c targets for people already diagnosed with diabetes are individualised — a tighter target may be appropriate for some people and less so for others, depending on age, risk of hypoglycaemia, kidney function, and life expectancy. Your GP will discuss your personal target with you.

Your GP will interpret your results in the context of your full medical history, your symptoms, your medications, and any previous results. A result outside the reference range does not automatically mean something is wrong, and a result within range does not always mean there is no problem. Always discuss your results with your GP or the clinician who ordered the test.