Prediabetes: what the result means and how it is found
Blood glucose that is raised but below the diabetes range usually comes with no symptoms. Here is how it is tested in Australia and what the guidance says.
Prediabetes means blood glucose is higher than normal but not high enough for a diagnosis of type 2 diabetes. It is found on a blood test, almost never by how someone feels. Diabetes Australia says the condition has no signs or symptoms, and Healthdirect explains what is going on underneath. The body's cells stop responding normally to insulin, the hormone that lets them use glucose for energy, and the pancreas makes more insulin to keep up. Glucose sits above the normal range during this stage without reaching the level at which diabetes is diagnosed.
Both organisations put the number of Australians with prediabetes at 2 million. Because most of them feel perfectly well, the testing rules matter more than any list of warning signs.
Two findings under one label
Prediabetes covers two related results. Impaired fasting glucose means glucose is raised after a period without food. Impaired glucose tolerance means glucose stays higher than it should after a measured dose of sugar. The Royal Australian College of General Practitioners' handbook on type 2 diabetes notes that the first is identified by a fasting blood glucose test and the second by a two-hour oral glucose tolerance test.
How many people are picked up depends on which test is used. In the Australian Bureau of Statistics' National Health Measures Survey 2022–24, which collected blood samples, 2.7% of adults had a fasting plasma glucose result that put them at high risk of diabetes. On the HbA1c test the figure was 4.8%. These were people who had not reported a diabetes diagnosis.
The three blood tests
Fasting blood glucose. Blood is taken from a vein after several hours without eating. The RACGP handbook classes a fasting result of 6.1 to 6.9 mmol/L as impaired fasting glucose. A result of 7.0 mmol/L or above is in the diabetes range.
HbA1c. This test measures how much of the haemoglobin in the blood has glucose attached to it. Healthdirect's page on the test describes it as showing average blood glucose over the past 8 to 12 weeks, and it needs no special preparation. A result of 6.5% (48 mmol/mol) or higher is used to diagnose diabetes, and a result below that may still suggest prediabetes. Anaemia, iron deficiency, kidney failure and pregnancy can all affect its accuracy, so the choice of test is one for the GP.
Oral glucose tolerance test. Diabetes Australia notes that any glucose test, fasting or not, that comes back higher than normal needs to be checked further, and that a doctor may then order this test. As the RACGP handbook sets it out, the person fasts for eight hours, gives a blood sample, drinks 75 g of glucose and gives a second sample two hours later. A two-hour result from 7.8 to 11.0 mmol/L is classed as impaired glucose tolerance. A result of 11.1 mmol/L or above is in the diabetes range.
One raised number is not always the end of the matter. For a person without symptoms, the handbook requires a second laboratory result that agrees with the first before diabetes is diagnosed. On cost, Healthdirect's guide to diabetes screening tests says that when a doctor orders the tests for someone with a Medicare card, they are usually bulk billed.
Who is advised to be checked
Healthdirect's guidance is that non-Indigenous Australians have their diabetes risk assessed every three years from the age of 40, using the Australian Type 2 Diabetes Risk Assessment Tool, known as AUSDRISK. A score of 12 or more is considered high risk. For Aboriginal and Torres Strait Islander people, screening blood tests are recommended once a year from the age of 18.
Some people are treated as higher risk whatever their score. Healthdirect's list includes those who have had a heart attack or stroke, women who have had gestational diabetes and women with polycystic ovary syndrome.
Diabetes Australia separates the risk factors a person can influence from those they cannot. In the first group are carrying excess weight around the waist (more than 94 cm for men and 80 cm for women), physical inactivity, high triglycerides with low HDL cholesterol, high blood pressure and smoking. In the second are having a first-degree relative with type 2 diabetes and certain family backgrounds, among them Aboriginal and Torres Strait Islander, Pacific Islander and South-East Asian.
Age runs through all of it. In the ABS National Health Survey for 2022, 6.1% of men and 5.2% of women aged 45–54 reported having diabetes. At 55–64 it was 11.8% of men and 10.5% of women. Among people aged 75 and over it was 20.7% and 17.2%. Type 2 was the most common form, accounting for 87.6% of cases.
What the guidance says about progression
Diabetes Australia estimates that, without sustained lifestyle changes, about 5–10% of people with prediabetes go on to develop type 2 diabetes each year. Healthdirect gives the figure as about 1 in 10. Diabetes Australia puts their risk at 10 to 20 times that of people with normal blood glucose, and Healthdirect adds that prediabetes also carries a greater risk of cardiovascular disease.
Progression is not inevitable. Diabetes Australia states that there is strong evidence type 2 diabetes may be prevented or delayed in up to 58% of cases through weight loss, healthy eating and regular exercise. That figure describes what happened across groups of people in research. It cannot say what will happen for any one person, and it is not a guarantee.
Diabetes Australia's advice comes as a short list:
- At least 30 minutes of moderate-intensity physical activity on most days, or three 20-minute sessions of vigorous exercise a week.
- Resistance training twice a week.
- A reduced energy (kilojoule) intake, with vegetables and fruit daily, lean proteins, and high-fibre carbohydrate foods such as wholegrain breads and cereals and legumes.
- Unsaturated fats in place of saturated fats, and limits on foods high in sugar, saturated fat and salt, on sugary drinks and on alcohol.
Healthdirect's summary is shorter still: eat a balanced diet, do more physical activity, and lose weight if overweight.
What to raise with a GP
It helps to arrive with specifics. It is reasonable to ask which test produced the result and what the number was, whether a second test is needed to confirm it, and when the next check should be. People who have not been tested and are 40 or older can ask for an AUSDRISK assessment at a routine visit.
Results depend on the test used and on a person's wider health. A GP is the right person to interpret an individual result and to say what, if anything, should follow from it.
Sources
- Diabetes Australia, Prediabetes.
- Healthdirect, Pre-diabetes.
- Healthdirect, Diabetes screening tests.
- Healthdirect, HbA1c test.
- Royal Australian College of General Practitioners, Management of type 2 diabetes: A handbook for general practice, Defining and diagnosing type 2 diabetes.
- Australian Bureau of Statistics, National Health Measures Survey, 2022–24.
- Australian Bureau of Statistics, Diabetes, 2022.
