Prediabetes means glucose is above normal but below the diabetes range, and where that line falls depends on which guideline your lab follows. Here is what the A1c, fasting and 2-hour numbers mean, how often prediabetes progresses, and what decades of prevention trials show.
A routine blood test comes back with a new word: prediabetes. It means your glucose is higher than normal but below the diabetes range 3, and it usually causes no symptoms 5.
The label is less fixed than it sounds. The ADA, Diabetes Canada and the World Health Organization (WHO) draw the lines in different places 1, 3, 10, and prediabetes does not always become type 2 diabetes. This article covers the ranges, who should be tested, how often prediabetes progresses, what prevention trials found and what “reversing” can mean.
Prediabetes covers three findings. Impaired fasting glucose (IFG) is a fasting glucose above normal after at least 8 hours without calories. Impaired glucose tolerance (IGT) is glucose above normal two hours after you drink 75 g of glucose in an oral glucose tolerance test (OGTT) 3. The third is a raised A1c, a blood test that shows your average blood sugar over the past 2 to 3 months 2. The WHO calls this in-between zone intermediate hyperglycaemia 10.
Prediabetes is not mild diabetes. Diabetes Canada notes that it does not carry the increased risk of damage to the small blood vessels of the eyes, kidneys and nerves seen in diabetes, but it does raise the risk of developing diabetes and cardiovascular disease. People with both IFG and IGT are at higher risk of both 3.
Most people feel nothing. Darker skin in the armpit or on the back and sides of the neck can be a sign. Frequent urination, intense thirst, hunger and fatigue can be early signs that prediabetes is turning into type 2 diabetes 5.
The tests that diagnose diabetes also diagnose prediabetes. A fasting test needs at least eight hours without eating. For an OGTT, you fast overnight, drink a sugary liquid at a lab and have your glucose measured over the next two hours 2. Our guide to mmol/L and mg/dL explains the two units.
| Test | ADA | Diabetes Canada | WHO |
|---|---|---|---|
| A1c | 5.7% to 6.4% 1 | 6.0% to 6.4% 3 | No range set below 6.5% 11 |
| Fasting glucose | 5.6 to 6.9 mmol/L (100 to 125 mg/dL) 1, 2 | 6.1 to 6.9 mmol/L (110 to 125 mg/dL) 3 | 6.1 to 6.9 mmol/L (110 to 125 mg/dL) 10 |
| Glucose 2 hours into a 75 g OGTT | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) 1, 2 | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) 3 | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) 10 |
Diabetes itself starts at an A1c of 6.5% (48 mmol/mol), a fasting glucose of 7.0 mmol/L (126 mg/dL) or a 2-hour value of 11.1 mmol/L (200 mg/dL) 1, 3. Only the 2-hour range for prediabetes is the same in all three systems.
The ADA’s fasting range starts at 5.6 mmol/L (100 mg/dL) 1, 2. In 2006, the WHO kept its cut-point at 6.1 mmol/L (110 mg/dL). It noted that a lower cut-point would sharply increase the number of people labelled, from 9.5% to 28.5% with IFG in US data, with no evidence that it reduced harm or progression to diabetes. The people it added had only about half the diabetes risk of those above 6.1 mmol/L 10. Diabetes Canada also uses 6.1 mmol/L because of the higher risk above that level 3.
The ADA’s A1c range starts at 5.7% (39 mmol/mol) 1. Diabetes Canada starts at 6.0% (42 mmol/mol), because levels of 6.0% to 6.4% carry a higher diabetes risk than levels of 5.5% to 6.0% 3. The WHO accepted A1c for diagnosing diabetes in 2011, but found the evidence insufficient for any formal recommendation on levels below 6.5% 11. A1c can also mislead in people with some hemoglobin variants or with hemolytic or iron-deficiency anemia 3, and in pregnancy 2. Our article on A1c, GMI and average glucose explains why A1c and glucose readings don’t always agree.
In plain terms: A fasting glucose of 5.9 mmol/L (106 mg/dL) or an A1c of 5.8% is prediabetes under the ADA’s cut-offs but not under Diabetes Canada’s. Before you compare your numbers with what you read online, check which ranges your lab report uses.
The CDC estimates that 115.2 million US adults have prediabetes, including 52.1% of people aged 65 or older 4. Johns Hopkins Medicine puts it as more than 2 in 5 US adults 12. More than 8 in 10 people who have it don’t know 5.
Mayo Clinic summarizes the ADA’s advice as screening for most adults from age 35, and before 35 for people with excess weight and other risk factors 2.
Diabetes Canada recommends assessing everyone’s risk of type 2 diabetes once a year. It recommends screening with a fasting glucose and/or A1c every 3 years from age 40, or for people at high risk on a risk calculator, meaning a 33% chance of developing diabetes over 10 years. People at very high risk, or with additional risk factors, may be tested every 6 to 12 months 13. Its risk factors include a parent, sibling or child with type 2 diabetes; African, Arab, Asian, Hispanic, Indigenous or South Asian descent; past gestational diabetes; high blood pressure; overweight or abdominal obesity; polycystic ovary syndrome; sleep apnea; and medicines such as glucocorticoids and atypical antipsychotics 13.
Once prediabetes is found, the ADA recommends checking for diabetes at least once a year, adjusted to each person’s risk 9.
It depends on which test is abnormal, by how much, and on age. A 2012 review in The Lancet estimated that 5% to 10% of people with prediabetes progress to diabetes each year, with about the same proportion returning to normal 6. In studies reviewed for the WHO’s 2006 report, the yearly risk of developing diabetes, compared with people with normal glucose tolerance, was about 6 times higher with IGT, 4.7 times with IFG alone and 12 times with both 10.
Trial control groups, recruited for high risk, show the upper end. In the US Diabetes Prevention Program (DPP), the placebo group developed diabetes at 11.0 cases per 100 person-years, or about 11 new cases for every 100 people followed for a year 7. In the Da Qing study in China, 67.7% of the control group had diabetes within six years 14.
Age changes the picture. A Johns Hopkins study followed 3,412 adults aged 71 to 90 for about six and a half years. Among those with prediabetes by A1c, 9% developed diabetes, 13% returned to normal and 19% died. Among those with IFG, the figures were 8%, 44% and 16% 15. The senior author, Elizabeth Selvin, said that in older adults, prediabetes “is just not a robust diagnosis” 15.
Three large randomized trials tested whether changing daily habits could keep prediabetes from becoming diabetes.
The DPP enrolled 3,234 US adults with raised glucose but no diabetes. Their average age was 51 and their average body mass index (BMI) 34.0 7. They were randomly assigned to placebo, metformin 850 mg twice a day, or an intensive lifestyle program aiming for at least 7% weight loss and at least 150 minutes of physical activity a week. Over an average of 2.8 years, diabetes developed at 11.0, 7.8 and 4.8 cases per 100 person-years in those three groups. That is 58% fewer cases with the lifestyle program and 31% fewer with metformin 7. Johns Hopkins Medicine notes that a structured lifestyle program cut the risk by 71% in people over 60 12.
The lifestyle group’s advantage shrank but lasted. Its risk was 27% lower than placebo at 15 years and 24% lower at 21 years 9. In the 21-year analysis, the metformin group’s risk was 17% lower (hazard ratio 0.83). Median time without diabetes was 3.5 years longer with the lifestyle program and 2.5 years longer with metformin, and the gaps between the groups narrowed over time 16.
The Finnish study randomized 522 middle-aged adults with overweight and IGT. Individual counselling in the intervention group targeted weight loss, less total and saturated fat, more fibre and more activity. After four years, 11% of the intervention group and 23% of the control group had diabetes, a 58% lower risk 17. At seven years, the reduction was 43% 9.
In 1986, researchers in Da Qing, China, screened 110,660 people and found 577 with IGT. Thirty-three clinics were randomly assigned to diet, exercise, diet plus exercise or a control group for six years. Diabetes developed in 67.7% of the control group, compared with 43.8%, 41.1% and 46.0% in the diet, exercise and combined groups. After adjusting for differences at the start, the risk reductions were 31%, 46% and 42% 14. At 30 years, the reduction was still 39% 9.
The ADA’s 2026 Standards of Care recommend referring adults with overweight or obesity who are at high risk of type 2 diabetes to a diabetes prevention program. The aim is a weight loss of at least 5% to 7%, through a healthy reduced-calorie eating pattern and at least 150 minutes a week of moderate activity 9. In the DPP, each kilogram lost was linked to a 16% lower risk of progression over 3.2 years, and further analysis suggested more benefit from losing at least 7% to 10% 9.
Mayo Clinic describes the activity target as at least 150 minutes of moderate or 75 minutes of vigorous aerobic activity a week 2. In Da Qing, the exercise-only group’s risk fell by 46% 14. Our article on exercise and glucose explains how working muscle uses glucose.
The ADA recommends that metformin be considered for prevention in adults at high risk of type 2 diabetes, especially those aged 25 to 59 with a BMI of 35 or more, higher fasting glucose and higher A1c, as well as people who have had gestational diabetes 9. In the DPP, metformin worked as well as the lifestyle program in people with a BMI of 35 or more and in those aged 25 to 44. The ADA suggests periodic vitamin B12 checks in people who take metformin long term. It also notes that newer medicines, including semaglutide and tirzepatide, have lowered diabetes incidence in specific groups, but that there are no long-term data supporting any medicine other than metformin for the sole purpose of prevention 9. Whether a medicine fits is a question for your prescriber.
“Reversing” usually means getting results back into the normal range. By the ADA’s numbers, that is an A1c below 5.7%, a fasting glucose below 5.6 mmol/L (100 mg/dL) and a 2-hour value below 7.8 mmol/L (140 mg/dL) 1. A recent study called this remission and defined it with those ADA criteria 18.
Among 1,990 DPP participants, those who reached normal glucose at least once during the trial had a 56% lower risk of diabetes in the years that followed, whichever group they had been in 8. In that study, 275 of 2,402 DPP participants (11.5%) reached remission after one year. Over about 20 years, cardiovascular death or hospital care for heart failure occurred at 1.74 per 1,000 person-years in that group, compared with 4.17 in those who did not reach remission. Thirty years of Da Qing data showed a similar pattern 18. These are observational findings, so they show an association, not proof of cause.
The ADA uses 5.7% to 6.4% 1, and Diabetes Canada uses 6.0% to 6.4% 3. The WHO has made no formal recommendation for A1c levels below 6.5%, the cut point it accepts for diagnosing diabetes 11.
The ADA uses 5.6 to 6.9 mmol/L (100 to 125 mg/dL) 1, 2. Diabetes Canada and the WHO use 6.1 to 6.9 mmol/L (110 to 125 mg/dL) 3, 10. A fasting glucose of 7.0 mmol/L (126 mg/dL) or more is in the diabetes range 3.
Glucose can return to the normal range, and each year about as many people with prediabetes return to normal as progress to diabetes 6. In the DPP, reaching normal glucose even once was linked to a 56% lower risk of later diabetes 8. The risk does not vanish, so yearly checks still matter 9.
There is no fixed timeline. About 5% to 10% of people with prediabetes progress each year 6. In a Johns Hopkins study of adults aged 71 to 90, only 8% to 9% developed diabetes over about six and a half years 15.
Sometimes. In the DPP, metformin cut new cases of diabetes by 31%, compared with 58% for the lifestyle program 7. The ADA recommends considering it for adults at high risk, especially those aged 25 to 59 with a BMI of 35 or more 9. The decision belongs with your prescriber.
Prediabetes is diagnosed with lab tests, so your logs can’t confirm or rule it out. They can show the habits the prevention trials focused on. In Glyve’s day view, the glucose line shows your own target range shaded, with logged meals, exercise, sleep and stress placed on the line. You can log by typing, voice or photo, and each estimate is a draft you check before saving. The week view shows whether a pattern repeats. If you use a meter or sensor, Glyve reads glucose from Apple Health, and Dexcom and FreeStyle Libre readings through those companies’ sharing services. Glyve is not a medical device and gives no advice.
How we write about diabetes. Spotted a mistake? Email info@glyve.ca and we’ll check it against the source.
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