Prediabetes Blood Tests
The exact Australian thresholds for HbA1c, fasting glucose, and OGTT — what each result means, whether prediabetes is reversible, and how to monitor it.
The Quick Answer
Prediabetes is a metabolic state in which blood glucose is higher than normal but not yet high enough to diagnose type 2 diabetes. It is not a disease in itself — it is a window of opportunity. Without intervention, approximately 5–10% of people with prediabetes progress to type 2 diabetes every year; with effective lifestyle changes, many return to normal glucose levels entirely.
In Australia, prediabetes is diagnosed using any one (or combination) of three tests: HbA1c 6.0–6.4%, fasting glucose 6.1–6.9 mmol/L(impaired fasting glucose), or OGTT 2-hour glucose 7.8–11.0 mmol/L(impaired glucose tolerance). Each test detects slightly different aspects of glucose regulation, which is why they are often ordered together.
The Exact Numbers — Australian Diagnostic Thresholds
These thresholds are based on RCPA (Royal College of Pathologists of Australasia) and Australian Diabetes Society guidelines. Note that HbA1c can be reported in two units: NGSP/DCCT (%) and IFCC (mmol/mol). Modern Australian reports often show both.
HbA1c (glycated haemoglobin)
<6.0% (<42 mmol/mol)
6.0–6.4% (42–47 mmol/mol)
≥6.5% (≥48 mmol/mol)
Reflects average blood glucose over the past 8–12 weeks. No fasting required. Most convenient screening test. Australian RCPA threshold for prediabetes starts at 6.0%.
Fasting plasma glucose (FPG)
<6.1 mmol/L
6.1–6.9 mmol/L (IFG)
≥7.0 mmol/L
Requires 8 hours fasting. Blood drawn in the morning before any food. Simple, inexpensive. "IFG" = impaired fasting glucose. Must be confirmed on a second occasion for diabetes diagnosis.
OGTT 2-hour glucose
<7.8 mmol/L
7.8–11.0 mmol/L (IGT)
≥11.1 mmol/L
75g glucose drink after overnight fast, glucose measured 2 hours later. "IGT" = impaired glucose tolerance. Best test for detecting postprandial insulin resistance. Used for gestational diabetes screening.
Fasting insulin (µIU/mL)
<10–12 µIU/mL
12–25 µIU/mL (suggestive)
Variable (depends on beta-cell function)
Not used for diagnosis — used to detect insulin resistance. High fasting insulin with normal glucose is the earliest detectable stage of insulin resistance. Not always Medicare-rebatable.
HOMA-IR (calculated)
<2.0
2.0–3.5 (indicates insulin resistance)
>3.5 (significant resistance)
Calculated from fasting glucose and insulin: (insulin × glucose) ÷ 22.5. Useful in people with metabolic syndrome, PCOS, and fatty liver. Not a diagnostic criterion but an important context marker.
How Prediabetes Is Diagnosed — The Full Workup
AUSDRISK questionnaire — know your risk score
Before blood tests, the Australian Type 2 Diabetes Risk Assessment Tool (AUSDRISK) can estimate your 5-year risk using 10 simple questions. A score of 12+ suggests high risk. Your GP may initiate testing based on your score, or you can use the questionnaire yourself to decide whether to ask for testing. Available free at diabetesaustralia.com.au/ausdrisk.
HbA1c — the first-line screening test
HbA1c is the most convenient starting point — no fasting required and a single blood draw. It reflects average glucose over 8–12 weeks. An HbA1c of 6.0–6.4% (42–47 mmol/mol) confirms prediabetes by Australian RCPA criteria. Below 6.0% is normal. Important: HbA1c can be unreliable in people with haemoglobin variants (certain ethnic groups), iron deficiency anaemia, haemolytic conditions, or chronic kidney disease. In these cases, fasting glucose or OGTT may be more appropriate.
Fasting plasma glucose — confirms or adds detail
A fasting glucose (at least 8 hours without food) is often done alongside or instead of HbA1c. Impaired fasting glucose (IFG) of 6.1–6.9 mmol/L confirms prediabetes. For type 2 diabetes diagnosis (7.0 mmol/L or above), a second test on a different day is required unless classical symptoms are present. Most GPs will run both HbA1c and fasting glucose together for a complete picture.
OGTT — when HbA1c and fasting glucose are inconclusive
The oral glucose tolerance test (OGTT) is more sensitive for postprandial insulin resistance than fasting glucose or HbA1c. It is the test of choice in pregnancy (gestational diabetes screening at 24–28 weeks). It is also valuable when there is clinical suspicion of prediabetes despite normal fasting glucose — for example, in people with significant abdominal obesity, PCOS, or family history of type 2 diabetes.
Fasting insulin and HOMA-IR — detecting early insulin resistance
Fasting insulin and HOMA-IR can detect insulin resistance before glucose levels rise — the earliest detectable stage of the prediabetes-to-diabetes continuum. Not part of standard diagnostic criteria, but increasingly used by GPs and metabolic health physicians as a proactive assessment tool. May not always attract a Medicare rebate — check with your GP first.
Full metabolic panel — the complete picture
Prediabetes rarely exists in isolation. Your GP will typically check lipids (fasting cholesterol, LDL, HDL, triglycerides), blood pressure, kidney function (eGFR, creatinine), liver function (ALT, GGT — fatty liver is closely linked to insulin resistance), and urine albumin-creatinine ratio (early kidney protection check). This forms a metabolic syndrome assessment and guides preventive treatment priorities.
Medicare GP Management Plan and cycle of care
If you are diagnosed with prediabetes or type 2 diabetes, you may be eligible for a GP Management Plan (GPMP) which allows Medicare-rebated referrals to allied health professionals including a dietitian, exercise physiologist, and diabetes educator. The Annual Cycle of Care for diabetes includes 10 specific checks per year covered under Medicare. Ask your GP about these entitlements.
Signs and Symptoms of Prediabetes
Prediabetes is often called a “silent” condition because most people have no obvious symptoms. This is why routine blood glucose testing for at-risk groups is so important. The following may be present in some people with prediabetes or significant insulin resistance.
Usually no symptoms (the silent stage)
Prediabetes rarely causes noticeable symptoms — this is both the challenge and the opportunity. Because glucose is only mildly elevated, the body compensates effectively. Most people discover prediabetes incidentally on routine blood tests. This is why screening is so important.
Fatigue after meals
Some people with significant insulin resistance notice tiredness or sleepiness after carbohydrate-rich meals (postprandial fatigue). This reflects the glucose surge and the effort the pancreas makes to compensate with large insulin releases.
Increased thirst or urination
These are classic diabetes symptoms that typically appear when glucose levels are higher than in prediabetes. If you have these symptoms alongside prediabetes-range blood tests, request a repeat test — you may already be at the diabetes threshold.
Acanthosis nigricans
Dark, velvety patches of skin in skin folds (neck, armpits, groin) are a clinical sign of significant insulin resistance. Commonly seen in people with prediabetes and type 2 diabetes, especially in younger adults and those with PCOS.
Central weight gain
Abdominal (visceral) fat is both a cause and a consequence of insulin resistance. A waist circumference above 94cm in men or above 80cm in women (Australian Heart Foundation guidelines for Australian adults of European descent; lower thresholds apply for Asian backgrounds) significantly increases prediabetes risk.
Brain fog or poor concentration
Insulin resistance in the brain may contribute to difficulty concentrating and brain fog, especially after high-carbohydrate meals. This is an emerging research area, not yet a well-established diagnostic criterion, but commonly reported by people with prediabetes and metabolic syndrome.
Red Flags — When to Seek Prompt Review
HbA1c ≥6.5% or fasting glucose ≥7.0 mmol/L
These values — confirmed on a repeat test — meet the diagnostic criteria for type 2 diabetes in Australia. Prediabetes management is replaced by formal diabetes care, medication review, and comprehensive monitoring. Your GP will refer you to a diabetes educator and may start medication.
Symptoms of hyperglycaemia alongside prediabetes-range results
If you have noticeable thirst, frequent urination, unexpected weight loss, or blurred vision alongside a prediabetes-range result, you may actually be at the diabetes threshold. Symptoms suggest more significant glucose elevation than the test result indicates — repeat testing promptly.
Prediabetes in pregnancy
Any glucose elevation in pregnancy requires specialist (obstetric or endocrinological) review. Gestational diabetes is treated differently and has implications for both mother and baby including birth weight, birth complications, and long-term diabetes risk for both.
Prediabetes with significant proteinuria or elevated creatinine
Early kidney changes (microalbuminuria or elevated creatinine) alongside prediabetes suggest that metabolic damage has already begun. This changes the risk profile and may prompt earlier pharmacological treatment (e.g., metformin, or even an SGLT2 inhibitor for renoprotection) rather than lifestyle alone.
Rapid progression from normal to prediabetes
If HbA1c or fasting glucose has moved from clearly normal to prediabetes over 12 months, the trajectory suggests active beta-cell stress. More frequent monitoring (every 3–6 months) and aggressive lifestyle intervention are warranted. Discuss with your GP whether early metformin is appropriate.
What to Do With a Prediabetes Diagnosis
The Diabetes Prevention Program (DPP) evidence base is clear: lifestyle is the most effective treatment for prediabetes. Medication (metformin) is sometimes added but is second-line.
Weight — the single biggest lever
Losing 5–7% of body weight reduces progression to type 2 diabetes by approximately 58% in people with IGT (impaired glucose tolerance). For a person weighing 90 kg, that is 4.5–6.3 kg — a realistic goal over 3–6 months. Even modest weight loss meaningfully improves insulin sensitivity. For people with severe obesity (BMI ≥35), bariatric surgery can achieve remission of prediabetes in the majority of cases.
Exercise — 150 minutes per week is the evidence-based target
The DPP used 150 minutes per week of moderate-intensity exercise (equivalent to brisk walking for 30 minutes, 5 days per week). Combining aerobic exercise with resistance training is more effective than aerobic exercise alone. Exercise improves insulin sensitivity independently of weight loss — even a single session of moderate exercise improves glucose uptake for 24–48 hours. Reducing prolonged sitting time also helps.
Diet — no single approach is best, but patterns matter
No single diet has been proven superior for prediabetes, but the common thread in successful interventions is: more vegetables, legumes, and whole grains; less refined carbohydrates and ultra-processed foods; less added sugar; and adequate lean protein. Reducing saturated fat was the original DPP dietary target. Low-carbohydrate and Mediterranean eating patterns have also shown benefit. An accredited practising dietitian can help tailor an approach to your preferences and lifestyle — Medicare rebates apply under a GP Management Plan.
Metformin — when is it appropriate?
Metformin is the most widely studied medication for prediabetes. The DPP showed it reduced progression by 31% (compared to 58% for lifestyle). Australian guidelines consider metformin in people with prediabetes who are under 60, have a BMI ≥35 kg/m², or have not responded to 3–6 months of structured lifestyle intervention. It is not PBS-listed for prediabetes in Australia (it is listed for type 2 diabetes), so it may be prescribed as a private script or as part of a shared care plan. Ask your GP.
Monitoring cadence — how often should you be tested?
Australian Diabetes Society guidelines recommend testing HbA1c or fasting glucose every 12 months in people with confirmed prediabetes. If you are actively working on lifestyle changes, your GP may check every 3–6 months to monitor progress and provide encouragement. If glucose normalises, annual testing should continue because prediabetes can recur with weight regain or lifestyle changes.
When Prediabetes Becomes Type 2 Diabetes
Progression from prediabetes to type 2 diabetes occurs when the pancreatic beta cells can no longer compensate for insulin resistance — insulin output falls, and glucose rises above the diagnostic threshold. This process is gradual and often takes years.
Diabetes is diagnosed in Australia when:
HbA1c ≥6.5% (48 mmol/mol) on two separate occasions, OR
Fasting plasma glucose ≥7.0 mmol/L on two separate occasions, OR
2-hour OGTT glucose ≥11.1 mmol/L, OR
Any of the above once, PLUS classical symptoms (thirst, polyuria, weight loss)
Once diabetes is diagnosed, management shifts to a comprehensive program including regular HbA1c monitoring, the annual diabetes cycle of care, medication initiation as appropriate (metformin, then additional agents as needed), and screening for diabetes-related complications (eyes, kidneys, feet, cardiovascular).
Foods That Support Healthy Blood Glucose
Non-starchy vegetables (broccoli, spinach, capsicum)
Low glycaemic loadThe foundation of a prediabetes-friendly diet. Fill half your plate at every meal. High fibre, low sugar, rich in magnesium and antioxidants that support insulin sensitivity.
Legumes (lentils, chickpeas, kidney beans)
Low GI + high fibreOne of the best carbohydrate sources for people with prediabetes. Slow glucose absorption, high protein, and rich in resistant starch that feeds beneficial gut bacteria and improves insulin sensitivity.
Whole grains (oats, barley, brown rice)
Lower GI than refined grainsBeta-glucan in oats and barley is among the best-evidenced dietary fibres for improving postprandial glucose. Replacing white bread and white rice with whole grain versions improves HbA1c over time.
Oily fish (salmon, sardines, mackerel)
Omega-3 + proteinReduces inflammation, supports cardiovascular health (a major co-risk with prediabetes), and provides protein without raising blood glucose. NHMRC recommends 2–3 serves per week.
Nuts and seeds (almonds, walnuts, chia)
Healthy fats + fibreSlow gastric emptying and improve postprandial glucose response. A small handful of almonds before a carbohydrate-containing meal measurably reduces the glucose spike. High in magnesium, which plays a role in insulin function.
Avocado
Monounsaturated fat + fibreRich in oleic acid and fibre, avocado slows carbohydrate absorption and improves the lipid profile. Pairs particularly well with higher-GI foods to blunt their glucose impact.
Berries (blueberries, strawberries, raspberries)
Low glycaemic, high antioxidantNaturally low in sugar relative to other fruits. Rich in anthocyanins which have been shown in some studies to improve insulin sensitivity. A good choice for satisfying sweet cravings.
Greek yoghurt and fermented dairy
Protein + probioticsHigher protein than regular yoghurt, lower in lactose. Some evidence links regular yoghurt consumption with reduced type 2 diabetes risk. Choose plain varieties without added sugar.
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This page provides general educational information about prediabetes and blood glucose testing in Australia. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your GP about your blood test results and diabetes risk. SmarterBlood does not provide medical care.