Fasting Glucose
Fasting glucose measures the sugar in your blood after an overnight fast. It is one of the main tests used as part of screening for pre-diabetes and type 2 diabetes — checking how well your body handles blood sugar when it has had nothing to work with for 8 hours. A single result is a snapshot; your GP usually looks at it alongside a longer-term blood-sugar average before drawing any conclusions.
Standard CareAustralians currently live with diabetes, and an estimated 2 million more are at high risk of developing type 2 diabetes.
What is fasting glucose?
Fasting glucose is the concentration of glucose — the main sugar your body uses for energy — circulating in your bloodstream after you have gone without food for at least 8 hours, usually overnight. A fasting sample is used because it removes the noise of recent meals: a casual (random) glucose check is harder to interpret because what you ate an hour earlier can shift the number significantly. Fasting glucose is one of the simplest and most widely used markers of how your body regulates blood sugar.
Why is it tested?
A fasting glucose test is there to answer a simple but important question: "Is my body managing blood sugar well?" In Australia, GPs use it as part of screening for diabetes, as part of routine health checks, and to investigate symptoms such as increased thirst, frequent urination, or unexplained fatigue. It is quick and inexpensive — a common first step in diabetes screening. Diabetes is never confirmed on a single result alone. Your GP looks at it alongside your history, symptoms, and any follow-up testing before reaching a conclusion.
Reference range (Australia)
Australia uses the WHO/NHMRC definition, so 6.1 (not the US/ADA 5.6) is the lower limit of pre-diabetes. A result of 7.0 mmol/L or above suggests diabetes is likely but does not confirm it on its own. Use the interval printed on your own report; it can vary slightly between laboratories.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A lower-than-range fasting glucose is less common. It can relate to a longer-than-usual fast, recent vigorous exercise, or alcohol. Certain medicines — insulin and some diabetes tablets in particular — can also bring it down below the expected range. A very low blood sugar (doctors call this hypoglycaemia) can cause shakiness, sweating, or confusion. If you had symptoms or your result is unexpectedly low, it is worth raising with your GP, who can look into what is behind it.
A fasting glucose within the normal range (about 3.0–6.0 mmol/L in Australia) is reassuring — it suggests your body is regulating blood sugar well during fasting. A normal result does not rule out future risk on its own. If you have risk factors such as a family history of diabetes, higher weight, or low physical activity, your GP may still suggest an HbA1c (a blood-sugar average over 2–3 months) or an oral glucose tolerance test (OGTT — a check of how your body handles a sugar load) for a fuller picture.
A higher-than-range fasting glucose means more sugar is circulating in your blood after fasting than expected. In Australia, a fasting result of 6.1–6.9 mmol/L falls in the impaired fasting glucose (IFG) range — also called pre-diabetes — and 7.0 mmol/L or above falls in the diabetes range, where diabetes is likely. A single raised result does not, by itself, mean you have diabetes — it is confirmed with a repeat test or further assessment; your GP will also weigh up your symptoms, your HbA1c (a longer-term blood-sugar average), and your individual risk factors. Short-term stress, illness, or a slip in fasting can also lift a reading. A raised result is worth a conversation with your GP to work out what is driving it.
What can affect your result
Fasting glucose reflects two things: how sensitive your body is to insulin (the hormone that moves sugar out of your blood), and how much insulin your pancreas is producing. When either is off, glucose can climb. Genuine fasting status also matters — food, sugary drinks, or even a minor slip before the test can push the number up. Acute stress, illness, infection, poor sleep, and the time of day can all shift a single reading. On the medicines side, corticosteroids, some beta-blockers, and certain antipsychotics can raise glucose; others, such as metformin and insulin, lower it. Glucose also tends to creep up gradually with age. Because any one reading is a snapshot, your GP usually looks at the pattern over time — often alongside HbA1c, which captures your average blood sugar over the past 2–3 months.
When to act
If your fasting glucose falls in the impaired fasting glucose (IFG) range (6.1–6.9 mmol/L) or in the diabetes range (7.0 mmol/L or above), the number alone is not enough to act on — bring it to your GP so the full picture can be assessed. A result between 5.5 and 6.0 mmol/L is not IFG, but it can signal increased risk if other risk factors are present; worth mentioning at your next visit. Your GP can confirm what the result means with a repeat test, an HbA1c, an oral glucose tolerance test (OGTT), or other checks, and walk through what your individual circumstances mean for you. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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