Your blood test comes back with an asterisk next to glucose: 108 mg/dL. Or with a glycated haemoglobin of 5.9%. Nothing hurts, you have not noticed anything unusual and the report does not say "diabetes" either. At most, it says the value is a little high. That middle ground has a name, prediabetes, and it is the point at which you have the most room to change course.
14 November is World Diabetes Day, and the theme the International Diabetes Federation has chosen for 2026 and 2027 is exactly that: early action on diabetes. We go through which fasting glucose, glycated haemoglobin (HbA1c) and glucose tolerance test results point to prediabetes, why the same result can carry one label on one report and another on the next, who should get tested and what has actually been shown to slow it down or reverse it.
In this article
The essentials in one minute
- Prediabetes means blood glucose above normal that has not yet reached diabetes. It hardly ever causes symptoms: it is found on a blood test.
- Under the American Diabetes Association criteria, prediabetes is a fasting glucose of 100 to 125 mg/dL, an HbA1c of 5.7 to 6.4% or a glucose of 140 to 199 mg/dL two hours into a glucose tolerance test. The WHO and the Spanish consensus set the fasting threshold at 110.
- Each year, between 5% and 10% of people with prediabetes go on to develop type 2 diabetes. Within 3 to 5 years, one in four returns to normal values.
- In the DPP trial, losing 7% of body weight and being active for 150 minutes a week cut new cases of diabetes by 58%.
- If you have prediabetes, repeat your fasting glucose and HbA1c once a year.
- At Clínica Eupnea in Palamós we run the full glucose profile, and our endocrinology and nutrition team supports you.
What prediabetes is
Prediabetes is an in-between state: blood glucose is above normal but below the threshold for diabetes. The World Health Organization describes it as a transition between normal values and diabetes, with a high risk of progressing to type 2 diabetes that, it stresses, can be prevented.
Behind it there is almost always insulin resistance. Insulin is the hormone that moves glucose into cells. When the liver and muscles respond to it less well, the pancreas makes more to compensate, and for years it half succeeds: glucose rises a little without reaching diabetic levels. If the pancreas wears out, type 2 diabetes sets in.
Impaired fasting glucose and impaired glucose tolerance: the two faces of prediabetes
There are two ways of being in prediabetes, and they can go together. Impaired fasting glucose is blood sugar that is slightly high in the morning, before breakfast. Impaired glucose tolerance is blood sugar that rises too much after a glucose load and takes too long to come down. According to the consensus of the Spanish Diabetes Society (SED), people who have both at once are twice as likely to end up with diabetes as those with only one.
HbA1c is a third route, and the same consensus points out a practical detail: fasting glucose, the glucose tolerance test and HbA1c do not pick up exactly the same people. That is why one test can come back fine while another does not.
Does prediabetes cause symptoms?
Hardly ever. According to MedlinePlus, the information service of the US National Library of Medicine, most people with prediabetes do not know it because they do not feel anything. Sometimes the skin gives a clue: darker, velvety patches in the armpits or on the back and sides of the neck, which doctors call acanthosis nigricans and which may come with small skin growths in the same areas.
If, on the other hand, you are very thirsty, passing a lot of urine, very tired or your vision is blurred, do not think prediabetes. These are the typical symptoms of diabetes that the WHO highlights in this year's campaign, and it is worth seeing a doctor without waiting for your next check-up.
Prediabetes values: how to read the fasting glucose and HbA1c on your blood test
Three tests are used for diagnosis. These are the American Diabetes Association (ADA) cut-offs, the ones MedlinePlus uses. Spanish laboratories report glucose in mg/dL, so we give the mmol/L equivalent in brackets:
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose | Below 100 mg/dL (5.6 mmol/L) | 100 to 125 mg/dL (5.6 to 6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or more |
| Glycated haemoglobin (HbA1c) | Below 5.7% | 5.7 to 6.4% | 6.5% or more |
| Glucose tolerance test (2 hours after drinking 75 g) | Below 140 mg/dL (7.8 mmol/L) | 140 to 199 mg/dL (7.8 to 11.0 mmol/L) | 200 mg/dL (11.1 mmol/L) or more |
American Diabetes Association criteria. Diabetes is confirmed with a second test on another day, unless glucose is very high or there are clear symptoms.
Why one report can say prediabetes and another not
The cut-offs are not universal, and that causes a lot of confusion. The WHO only speaks of impaired fasting glucose from 110 mg/dL (6.1 mmol/L). The SED consensus on prediabetes, drawn up with the Spanish family medicine and endocrinology societies and published in 2015, also uses 110 for fasting glucose, although it accepts the ADA's HbA1c range of 5.7 to 6.4%. France follows the WHO criterion: 1.10 to 1.25 g/L, according to the French Diabetes Federation. And the UK's NICE guideline treats an HbA1c of 6.0 to 6.4% (42 to 47 mmol/mol) as high risk.
So a fasting glucose of 104 mg/dL is prediabetes by the American criterion and normal by the WHO's. That does not mean one laboratory is wrong. Risk rises continuously, and each scientific society draws the line in a different place. What matters is how far you are from normal, whether the result repeats and what other risk factors you have.
Fasting, repeat tests and other details that change the result
- Fasting glucose requires at least 8 hours without eating or drinking anything other than water.
- A single value is not enough. Diabetes is confirmed with a second test on another day, and prediabetes is also worth checking again.
- HbA1c reflects your average glucose over the last two or three months and needs no fasting. A bad day, a cold or a stressful spell, which can push a one-off glucose reading up, do not change it either.
- But HbA1c can be unreliable with anaemia or other red blood cell disorders, kidney failure or liver disease, and it is not used to diagnose diabetes in pregnancy.
The glucose tolerance test: it sees what fasting glucose misses
The glucose tolerance test (oral glucose load) involves measuring fasting glucose, drinking a solution with 75 grams of glucose and measuring again two hours later. It is the only one of the three tests that detects impaired glucose tolerance.
This is not a minor point. In the di@bet.es study, the most common form of prediabetes in Spain was precisely isolated impaired glucose tolerance, in 9.2% of adults, and it only shows up on this test. In addition, as the SED consensus notes, some authors advise doing the test in people with impaired fasting glucose, because in a third of cases diabetes is already present.
How many people have prediabetes (and why almost nobody knows)
Diabetes keeps growing. According to the WHO, 830 million people were living with diabetes in 2022, 14% of the world's adults and twice the 1990 figure, and this year's campaign points out that more than 40% of people with diabetes are undiagnosed.
In Spain, the di@bet.es study, the first one carried out on a sample representative of the whole country, found that almost 30% of adults had some form of glucose disorder: 13.8% had diabetes (almost half without knowing it) and another 14.8% had prediabetes. The data were collected in 2009 and 2010, with a glucose tolerance test for every participant and fasting glucose assessed against the WHO threshold of 110. The American threshold of 100 would have produced more cases.
In Catalonia, Canal Salut, the Catalan health portal, estimates that more than 630,000 people have diabetes: 9% of the population aged 15 and over, according to the 2022 Catalan Health Survey.
Does prediabetes always lead to diabetes?
No, and it is worth being clear about this, because many people experience it as a sentence. These are the figures in the SED consensus. With normal glucose, the risk of developing type 2 diabetes is about 0.7% a year. With impaired fasting glucose or impaired glucose tolerance, it rises to 5-10% a year. But the road runs both ways: over 3 to 5 years, roughly one in four people with prediabetes goes on to develop diabetes, another one in four returns to normal and half stay the same.
Getting back to normal, even for a while, counts. In the long-term follow-up of the US Diabetes Prevention Program trial, people who reached normal glucose at least once later had a 56% lower risk of diabetes than those who always stayed in prediabetes.
And it is not only about sugar. Observational studies link prediabetes to early damage in the kidneys, nerves and retina, and to higher cardiovascular risk, partly because it tends to come with high cholesterol, high blood pressure, smoking or excess weight. If your cholesterol is also high, you may find our article on how to read the cholesterol on your blood test useful.
Risk factors for prediabetes
You are more likely to have prediabetes if:
- you are overweight or have obesity, especially if fat builds up around your waist: the SED consensus considers a waist above 102 cm in men and 88 cm in women a risk;
- you are 45 or older;
- your father, your mother or a brother or sister has diabetes;
- you do little physical activity;
- you have high blood pressure or high cholesterol or triglycerides;
- you had diabetes during pregnancy;
- you have polycystic ovary syndrome;
- you have had a heart attack or a stroke;
- you take medicines that raise glucose, such as corticosteroids or some antipsychotics.
Weight does not explain everything. Diabetes UK points out that prediabetes also occurs in people of a healthy weight.
Who should get tested for prediabetes, and how often
There is no single schedule. The SED consensus offers two routes:
- a fasting glucose every 4 years from the age of 45, taking advantage of routine blood tests, and every year if you have risk factors like those in the list above;
- or starting with a questionnaire, the FINDRISC test, every 4 years from the age of 40 (or between 25 and 39 if there are risk factors), and doing the blood test when the score is high.
If you have already been told you have prediabetes, the schedule changes: the same consensus advises checking fasting glucose and HbA1c every year. The UK's NICE guideline agrees and recommends a blood test at least once a year for people at high risk.
In our general medicine clinic, the annual preventive check-up includes a full blood test and a blood pressure reading, plus an electrocardiogram from the age of 40.
The FINDRISC test: 8 questions to work out your risk
FINDRISC is a validated questionnaire developed in Finland that needs no blood test. It asks about your age, body mass index, waist circumference, physical activity, whether you eat fruit or vegetables every day, whether you take blood pressure medication, whether high glucose has ever been found and whether there is diabetes in your family. It gives a score from 0 to 26. At 15 or more the risk is considered high, and the SED consensus advises a fasting glucose test.
It has its limits, and the consensus itself acknowledges them: many people do not know how to calculate their body mass index, and waist circumference is not usually measured in clinics. If in doubt, fasting glucose and HbA1c come from a single blood sample.
How to reverse prediabetes: what has been shown to work
The strongest evidence comes from the Diabetes Prevention Program (DPP) trial, published in 2002 in the New England Journal of Medicine. It included 3,234 adults with raised glucose, with an average age of 51 and, on average, obesity. One group was asked to lose at least 7% of their body weight and do 150 minutes of physical activity a week; another took metformin and a third, a placebo.
Over almost three years, the lifestyle programme cut new cases of diabetes by 58%, and metformin by 31%. Put another way: 7 people had to go through the lifestyle programme to prevent one case of diabetes over three years, and 14 had to take metformin.
The effect fades over the years but does not disappear. At 15 years, the reduction was still 27% with lifestyle changes and 18% with metformin, although by then more than half of the participants in every group had developed diabetes. A review published in The Lancet in 2012 puts the relative risk reduction from lifestyle changes at between 40% and 70%.
Losing 7% of your weight, if you have weight to lose
You do not need to reach your ideal weight. The DPP target was 7%, and the SED consensus talks about losing between 5% and 10%. For someone weighing 90 kilos, 7% is just over 6 kilos. The same consensus stresses that the weight loss that lasts is slow and gradual, and that the hardest part comes afterwards: keeping it off.
If your weight is already normal, the aim is not to slim down. As Diabetes UK explains, not everyone with prediabetes needs to lose weight.
Moving for 150 minutes a week (walking counts)
The WHO recommends at least 150 minutes a week of moderate activity to prevent type 2 diabetes. The SED consensus puts this as 30 minutes a day on at least five days a week, or 90 minutes a week if the exercise is vigorous, and advises combining aerobic exercise with strength exercises.
The right pace is one at which it is hard to keep up a conversation. Brisk walking, swimming, cycling or climbing stairs all count. And it helps even if you do not lose weight: according to the French Diabetes Federation, in people with prediabetes physical activity on its own reduces the risk of diabetes by 30% to 50%, regardless of diet and weight, and low-intensity activity adds up too.
What to eat: the Mediterranean pattern, without giving up fruit
There is no special diet for prediabetes. What the SED consensus recommends is very close to what people on this coast have always eaten: limiting fast-absorbing carbohydrates (sugar, sweets, juices) and saturated fat (red meat, cured meats, pastries); eating fruit, vegetables, pulses, wholegrain cereals and low-fat dairy; and using extra virgin olive oil as the main fat, with nuts and olives.
In the Spanish PREDIMED study, carried out in people aged 55 to 80 at high cardiovascular risk, a Mediterranean diet with extra virgin olive oil, without counting calories, was followed by fewer new cases of diabetes than a low-fat diet. It is a secondary analysis of a trial that had to be revised in 2018 because some participants had not been randomised as planned, so it is best read as supporting evidence rather than final proof.
You will find more ideas in our article on the Mediterranean diet, and in our dietetics and nutrition clinic we help you adapt it to your schedule and your tastes.
Smoking and medicines that raise glucose
Not smoking is part of the prevention the WHO recommends. And if you take corticosteroids, some antipsychotics or other medicines that can raise glucose, mention it to your doctor, because the SED consensus counts them among the risk factors. Never stop them on your own.
Do you need medication for prediabetes?
Usually not. The foundation is lifestyle, which worked better than metformin in the DPP. According to the American Diabetes Association recommendations quoted in the SED consensus, metformin is considered in very high-risk situations, such as severe obesity (a body mass index of 35 or more) in people under 60, or previous diabetes in pregnancy. It is a decision made with the endocrinologist, case by case.
Myths about prediabetes
"If I don't feel anything, it can't be important." Prediabetes hardly ever causes symptoms, and each year between 5% and 10% of people who have it progress to diabetes. The fact that you cannot feel it is precisely the reason to look for it.
"I'll have to give up fruit." Whole fruit is part of what is recommended. What is worth limiting is sugar, sweets and juices.
"It only happens to people who are overweight." It is more common with excess weight, but it also occurs at a normal weight.
"If one blood test comes back fine, that's it." Getting back to normal greatly reduces the risk, but it is worth carrying on with a yearly check.
"It's practically diabetes already, whatever I do." One in four people with prediabetes returns to normal values within 3 to 5 years, and lifestyle changes reduce the risk of diabetes by between 40% and 70%.
How we can help at Clínica Eupnea
In Palamós you have the whole pathway in one centre:
- the glucose profile in our metabolic studies: fasting glucose, glycated haemoglobin (HbA1c) and the glucose tolerance test, to diagnose diabetes, prediabetes and insulin resistance and to monitor them;
- routine blood tests, with biochemistry (glucose, cholesterol, triglycerides, kidney and liver function) and, if needed, the hormone profile, which includes insulin;
- the endocrinology clinic with Dr David Pérez Asensio, who interprets the results, looks into the causes of obesity when it is present and decides whether treatment is needed;
- the dietetics and nutrition clinic with Ms Yolanda Jiménez Monroig, who prepares personalised eating plans to lose weight sustainably or to control glucose;
- general medicine with Dr Josep Ausio, for the yearly check-up and for keeping an eye on blood pressure and cholesterol.
If you already have diabetes, you may find our guide to the types of diabetes and their treatment and our article on diabetic foot care useful.
Endocrinologist and glucose testing in Palamós
Book an appointment on 872 21 75 91 or by WhatsApp on 650 489 884, Monday to Friday from 9.00 to 13.30 and from 15.30 to 19.30, at Passeig del Mar, 41, Palamós. For fasting glucose and the glucose tolerance test, come after fasting for at least 8 hours; for HbA1c on its own there is no need.
Frequently asked questions
Yes, and it often is. According to the Spanish Diabetes Society consensus, within 3 to 5 years about one in four people with prediabetes goes back to normal values. In the DPP trial, losing 7% of body weight and being active for 150 minutes a week cut new cases of diabetes by 58%, and people who managed to bring their glucose back to normal later had a 56% lower risk.
Using the American Diabetes Association criteria: a fasting glucose of 100 to 125 mg/dL (5.6 to 6.9 mmol/L), an HbA1c of 5.7 to 6.4%, or a glucose of 140 to 199 mg/dL (7.8 to 11.0 mmol/L) two hours after drinking 75 grams of glucose. The WHO and the Spanish Diabetes Society consensus only speak of impaired fasting glucose from 110 mg/dL (6.1 mmol/L), and the UK's NICE guideline considers an HbA1c of 6.0 to 6.4% (42 to 47 mmol/mol) high risk.
Hardly ever, which is why it is usually picked up on a blood test. Sometimes patches of darker, velvety skin appear on the neck or in the armpits. If you are very thirsty, passing a lot of urine, very tired or your vision is blurred, see a doctor without waiting: these are typical symptoms of diabetes.
Once a year, with fasting glucose and HbA1c, according to the Spanish Diabetes Society consensus. The UK's NICE guideline also advises a blood test at least once a year for people at high risk. If symptoms appear, do not wait for the check-up.
Yes. Whole fruit, vegetables, pulses and wholegrain cereals are part of the recommended diet. What is worth limiting is fast-absorbing sugar, such as table sugar, sweets and juices, and the saturated fat in red meat, cured meats and pastries.
Usually not. The foundation is changes to diet, physical activity and weight, which worked better than metformin in the DPP trial. Metformin is kept for very high-risk situations, such as severe obesity in people under 60 or previous diabetes in pregnancy, and the decision is your doctor's.
They complement each other, because they do not pick up exactly the same people. Fasting glucose is simple, but it needs 8 hours of fasting and varies from day to day. HbA1c reflects the last 2 or 3 months and needs no fasting, although it is unreliable with some types of anaemia. The glucose tolerance test is the only one that detects impaired glucose tolerance.
Have you been told your glucose is a little high?
At Clínica Eupnea in Palamós we run the full glucose profile (fasting glucose, HbA1c and glucose tolerance test), and our endocrinology and nutrition team helps you bring it down.
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