High Blood Sugar Explained
What an elevated glucose result means on your blood test, whether you need to worry, and what your GP will do next — in plain Australian English.
What Does Elevated Fasting Glucose Mean?
A fasting blood glucose test measures the amount of sugar (glucose) in your blood after you have fasted for 8–12 hours. When you eat, your body breaks down carbohydrates into glucose, which enters the bloodstream. The hormone insulin, produced by your pancreas, moves glucose from the blood into your cells for energy.
When your fasting glucose is elevated, it means one of two things: either your pancreas is not producing enough insulin, or your cells are not responding to insulin properly (insulin resistance). In both cases, glucose stays in the blood instead of being used by cells.
Persistently elevated blood sugar damages blood vessels, nerves, kidneys, and eyes over time. This is why early detection matters — the damage from high blood sugar begins years before diabetes is formally diagnosed.
Diagnostic Thresholds — Normal, Pre-Diabetes, and Diabetes
These thresholds are based on the Australian Diabetes Society (ADS) and World Health Organisation (WHO) criteria, adopted by the RACGP.
Normal
HbA1c: < 42 mmol/mol (< 6.0%)
Blood sugar is well regulated. No further action needed unless risk factors are present.
Pre-diabetes (IFG)
HbA1c: 42 – 47 mmol/mol (6.0 – 6.4%)
Impaired fasting glucose. Your body is starting to lose its ability to regulate blood sugar. Lifestyle changes can reverse this.
Diabetes
HbA1c: ≥ 48 mmol/mol (≥ 6.5%)
Diagnostic threshold for diabetes when confirmed on two separate occasions. Your GP will discuss management options.
Comparing Blood Sugar Tests
There are several ways to measure blood sugar, and they each tell your GP something different.
What it measures
Blood sugar right now (after 8–12 hour fast)
Average blood sugar over the past 2–3 months
Blood sugar at any random time (no fasting)
Fasting required?
Yes (8–12 hours)
No
No
Affected by last meal?
Yes — that is the whole point
No — reflects long-term average
Yes — expected to be higher after eating
Diabetes threshold
≥ 7.0 mmol/L
≥ 48 mmol/mol
≥ 11.1 mmol/L with symptoms
Best for
Screening and initial diagnosis
Monitoring and confirming diagnosis
Emergency assessment only
Cost (Medicare)
Bulk-billed with GP referral
Bulk-billed with GP referral
Bulk-billed (usually done in hospital)
Common Non-Diabetic Causes of High Blood Sugar
An elevated glucose does not automatically mean diabetes. Several conditions and medications can raise blood sugar temporarily or permanently.
Acute stress or illness
Physical stress (infection, surgery, trauma) triggers cortisol and adrenaline release, which raises blood glucose as part of the fight-or-flight response. Hospital patients routinely have elevated glucose without having diabetes.
Corticosteroid medication
Prednisolone, dexamethasone, and other corticosteroids are the most common medication cause of hyperglycaemia. They reduce insulin sensitivity and increase hepatic glucose production. Even short courses (5–7 days) can spike glucose significantly.
Not actually fasting
The most common practical reason for an unexpectedly high result. Eating within 8 hours, or drinking juice or sweetened coffee, will elevate fasting glucose. Always tell the pathology collector if you were not truly fasting.
Cushing syndrome
Excess cortisol production from adrenal tumour, pituitary adenoma, or long-term steroid use. Cortisol drives insulin resistance. Often accompanied by weight gain, moon face, and easy bruising.
Pancreatitis
Inflammation of the pancreas damages insulin-producing beta cells. Acute pancreatitis from gallstones or alcohol can cause temporary hyperglycaemia. Chronic pancreatitis can lead to permanent diabetes (Type 3c).
Gestational changes
Placental hormones naturally increase insulin resistance in the second and third trimesters. This is why gestational diabetes screening (OGTT) is standard at 24–28 weeks in Australia.
What Happens After a High Result
Here is the typical pathway your GP will follow after an elevated fasting glucose result.
1. Confirm the result
A single elevated fasting glucose is not diagnostic. Your GP will request a repeat blood test (typically within 2–4 weeks) to confirm. You will be asked to fast properly for 10–12 hours before the repeat. If the second result is also elevated, an HbA1c will usually be ordered at the same time.
2. HbA1c test
This gives the 3-month average and avoids the variability of a single fasting glucose reading. If HbA1c is 42–47 mmol/mol, you are in the pre-diabetes range. If it is 48 mmol/mol or above, this is consistent with diabetes. No fasting required for this test.
3. Oral Glucose Tolerance Test (OGTT)
Sometimes ordered when results are borderline or when gestational diabetes is suspected. You fast overnight, drink a 75g glucose solution at the pathology lab, then have blood drawn at 1 and 2 hours. A 2-hour glucose of 11.1 mmol/L or above confirms diabetes.
4. Assess cardiovascular risk
Elevated blood sugar is strongly associated with cardiovascular disease. Your GP will typically check cholesterol, blood pressure, and kidney function at the same time. The Australian Absolute Cardiovascular Disease Risk calculator combines these factors to estimate your 5-year risk.
5. Lifestyle intervention (pre-diabetes)
If you are in the pre-diabetes range, the evidence is clear: lifestyle changes are more effective than medication at preventing progression. The landmark Finnish Diabetes Prevention Study showed 58% risk reduction with modest diet changes and 150 minutes/week of exercise. In Australia, the Life! program (funded by the Victorian Government) offers free support for people with pre-diabetes.
6. Medication discussion (diabetes)
If confirmed as diabetes, metformin is usually the first-line medication in Australia. It is PBS-listed, well tolerated, and has decades of safety data. Your GP will discuss whether medication is needed now or whether a trial of lifestyle changes is appropriate first. Diabetes Australia provides free resources and support.
Australian Diabetes Screening Guidelines
The RACGP and Diabetes Australia recommend blood sugar screening for all adults from age 40, repeated every 3 years. Earlier and more frequent screening is recommended if you have any of the following risk factors:
Family history of Type 2 diabetes (first-degree relative)
Aboriginal or Torres Strait Islander background (screen from age 18)
Pacific Islander, South Asian, Chinese, or Middle Eastern background
Body mass index (BMI) of 25 kg/m² or above, or waist circumference over 94 cm (men) or 80 cm (women)
History of gestational diabetes
Polycystic ovary syndrome (PCOS)
Previous impaired fasting glucose or impaired glucose tolerance
Cardiovascular disease, high blood pressure, or dyslipidaemia
Current use of antipsychotic or corticosteroid medication
Frequently Asked Questions
I had a fasting glucose of 5.8 mmol/L. Do I have diabetes?
No. A fasting glucose of 5.8 mmol/L falls in the pre-diabetes range (5.5–6.9 mmol/L), also called impaired fasting glucose (IFG). This means your body is starting to struggle with blood sugar regulation, but you have NOT crossed the diabetes threshold (7.0 mmol/L). The good news: pre-diabetes is reversible with lifestyle changes in many cases. Your GP will likely suggest a repeat test and HbA1c to confirm.
Can stress cause a high blood sugar reading?
Yes. Physical stress (illness, surgery, pain) and psychological stress both raise cortisol, which in turn raises blood glucose. If you were unwell, had a poor night of sleep, or were particularly anxious on the day of your blood test, your fasting glucose could be elevated by 0.5–2.0 mmol/L above your true baseline. This is why a single reading is never diagnostic — retesting under calm, well-rested conditions is standard practice.
What is the difference between fasting glucose and HbA1c?
Fasting glucose is a snapshot of your blood sugar right now (after fasting). It fluctuates throughout the day based on meals, stress, and activity. HbA1c measures the percentage of your haemoglobin (in red blood cells) that has glucose attached to it. Because red blood cells live for about 3 months, HbA1c gives a weighted average of your blood sugar over that period. HbA1c is more stable but less sensitive to recent changes.
My blood sugar was 6.2 mmol/L but I had coffee before my test. Is this accurate?
Coffee can raise fasting glucose by approximately 0.3–0.8 mmol/L due to the cortisol and adrenaline response caffeine triggers. If your true fasting glucose is around 5.5 mmol/L, coffee could push it to 6.2 mmol/L, making it look like pre-diabetes when it may actually be normal. Tell your GP you had coffee and request a proper fasting retest with only water beforehand.
Does Medicare cover diabetes screening blood tests?
Yes. In Australia, fasting glucose and HbA1c are fully covered by Medicare when requested by a GP. There is no out-of-pocket cost at bulk-billing pathology labs (Laverty, QML, Sullivan Nicolaides, etc.). The RACGP recommends screening every 3 years from age 40, or earlier if you have risk factors (family history, obesity, ATSI background, history of gestational diabetes, or PCOS).
Related Reading
Track Your Blood Sugar Over Time
Upload your blood test results and see your glucose and HbA1c trends charted automatically — so you and your GP can track progress together.
This information is based on guidelines from the Australian Diabetes Society (ADS), the RACGP, and the World Health Organisation (WHO). Diagnostic thresholds and screening recommendations follow current Australian practice. SmarterBlood provides educational information only and is not a substitute for professional medical advice.