Prediabetes is a fasting blood glucose above normal but below the diabetes threshold: an early, reversible signal that the French National Authority for Health (HAS) proposes to screen for with a fasting venous blood glucose test from age 45 when a risk factor is present. HbA1c reflects average blood glucose over the previous two to three months.
What is prediabetes?
Prediabetes, or impaired glucose regulation, is an intermediate state in which blood glucose is above the values considered normal without reaching the threshold that defines diabetes. It is not a disease but a risk factor: the HAS guidelines on the prevention and screening of type 2 diabetes (2014) describe it as the first of three phases in the course of the disease, followed by an asymptomatic phase of about ten years, then the clinical phase with its complications.
French National Health Insurance (Assurance Maladie) defines diabetes as “a chronic disease characterized by the presence of excess sugar in the blood, called hyperglycemia.” In France, in 2022, more than 4.3 million people were being treated for diabetes, or 6.3% of the population (Assurance Maladie), and, according to a 2016 survey cited by Inserm (the French National Institute of Health and Medical Research), nearly a quarter of people with the disease did not know they had it.
Prediabetes covers two situations, defined by the WHO in 2006 and adopted by the HAS:
- impaired fasting glucose: blood glucose between 1.10 g/l (6.1 mmol/l) and 1.25 g/l (6.9 mmol/l) after an eight-hour fast, confirmed on two occasions;
- impaired glucose tolerance: blood glucose between 1.40 g/l and 1.99 g/l two hours after ingesting 75 g of glucose.
The HAS guidelines note that prediabetes is associated with an increased later risk of stroke; its main characteristic remains that it is reversible.
Fasting blood glucose, HbA1c, glucose tolerance test: what does each test measure?
Three tests explore sugar regulation, with different time windows: fasting blood glucose is a snapshot of the moment, HbA1c summarizes the past two to three months, and the glucose tolerance test measures the response to a glucose intake.
| Test | What it measures | Conditions | Reference thresholds | Role in France |
|---|---|---|---|---|
| Fasting venous blood glucose | Glucose in the plasma at a given moment | 8-hour fast | Normal below 1.10 g/l; prediabetes 1.10 to 1.25 g/l; diabetes 1.26 g/l (7 mmol/l) or higher, confirmed on two occasions | Screening test recommended by the HAS |
| HbA1c (glycated hemoglobin) | The proportion of hemoglobin bound to glucose, reflecting average blood glucose over the previous 2 to 3 months | No fasting required | Diabetes 6.5% or higher and prediabetes 5.7 to 6.4% according to the American Diabetes Association (2010); not used for screening in France | Monitoring of people with diabetes, with an individualized target |
| Glucose tolerance test | Blood glucose 2 hours after ingesting 75 g of glucose | Fasting, in the laboratory, 2 hours | Impaired tolerance 1.40 to 1.99 g/l; diabetes 2 g/l or higher | Screening for gestational diabetes; special situations |
Two points about HbA1c. It can be skewed by anything that alters the lifespan of red blood cells or hemoglobin (anemia, hemoglobinopathies, kidney failure, pregnancy). And although the American Diabetes Association accepted it as a diagnostic tool in 2010, the HAS guidelines point out that in France, measuring glycated hemoglobin to screen for diabetes is not recommended: the screening test is fasting venous blood glucose. In a person with diabetes, however, HbA1c is the monitoring tool, with a target set with the doctor according to age and situation.
What are the risk factors for type 2 diabetes?
Type 2 diabetes results from a progressive resistance of the tissues to insulin, followed by exhaustion of insulin secretion. The HAS guidelines distinguish risk factors with a demonstrated causal link from mere risk markers.
| Risk factors with a demonstrated causal link (HAS 2014) | Risk markers, association without demonstrated causality (HAS 2014) |
|---|---|
| Age over 45 | High blood pressure |
| Non-Caucasian origin, or migrant background with adoption of a Western lifestyle | Dyslipidemia (low HDL or high triglycerides) |
| Excess weight (BMI above 28 kg/m²) | Chronic smoking |
| Sedentary lifestyle | |
| Family history of diabetes in a first-degree relative | |
| History of gestational diabetes, or of giving birth to a low-birth-weight baby | |
| Prediabetes |
French National Health Insurance adds concrete benchmarks: a body mass index of 25 kg/m² or more, a waist circumference of at least 94 cm in men and 80 cm in women, less than 30 minutes of physical activity per day, giving birth to a baby weighing more than 4 kg. The HAS also suggests using a validated questionnaire such as FINDRISK to identify people at risk: this is the type of tool a prevention check-up at ages 45–50 uses.
Who should be screened, and how often, according to the HAS?
The HAS recommends so-called “targeted opportunistic” screening, meaning screening offered during a contact with the healthcare system, for men and women aged 45 and over with at least one of the risk factors above. The test is fasting venous blood glucose; a result above the threshold is confirmed by a second test.
The frequency depends on the result (HAS guidelines, 2014):
- blood glucose below 1.10 g/l: neither diabetes nor prediabetes; repeat screening every 3 years, or every 1 to 3 years for people with several risk factors;
- blood glucose between 1.10 and 1.25 g/l: prediabetes; management of modifiable risk factors (diet, physical activity, weight) and repeat screening 1 year later;
- blood glucose of 1.26 g/l or higher, confirmed by a second test: diabetes; comprehensive care, including management of cardiovascular risk factors.
This screening is part of the prevention check-up at key ages, particularly at 45–50; blood glucose is part of any panel of blood biomarkers.
What does metabolomics add: glycolysis and branched-chain amino acids?
Metabolomics by nuclear magnetic resonance (NMR) measures, alongside glucose, other indicators of energy metabolism and amino acids whose levels deviate from normal years before a diabetes diagnosis. It does not replace fasting blood glucose; it describes the trajectory leading to it. Three families of findings.
- Branched-chain and aromatic amino acids. In 2011, Wang and colleagues showed in Nature Medicine, in 2,422 normoglycemic participants of the Framingham cohort followed for 12 years (201 new cases of diabetes), that five amino acids, isoleucine, leucine, valine, tyrosine and phenylalanine, were associated with the risk of future diabetes; a combination of three of them multiplied the risk more than fivefold in the highest quartile. The 2023 UK Biobank atlas adds nuance: high branched-chain amino acids go with a higher risk of metabolic diseases, but a lower risk for other diseases (Julkunen et al.).
- Glycolysis. In the multi-disease prediction study conducted in 117,981 UK Biobank participants, glucose and lactate dominated the metabolomic signature of type 2 diabetes, and the full profile added predictive information to age and sex for this disease (Buergel et al., Nature Medicine, 2022). In the 2023 atlas, alanine was mainly associated with the risk of diabetes and its complications.
- Fatty acids. In the same 2022 study, higher levels of docosahexaenoic acid (DHA) and linoleic acid were associated with a lower risk of diabetes: a bridge to our article on fatty acids and omega-3s.
What this changes in practice: in a person whose blood glucose is still normal, a telling metabolomic profile (high branched-chain amino acids and alanine, high lactate, low DHA, often with a high GlycA and a lipoprotein profile suggestive of insulin resistance) describes a trajectory on which habits have the greatest effect. These markers have no clinical threshold and do not establish any diagnosis; they are interpreted with a doctor, following the logic described in our article on NMR metabolomics.
Is prediabetes reversible?
Yes, to a large extent: the two landmark randomized trials showed that a structured lifestyle change reduced the onset of diabetes by 58% in people with prediabetes, a result the HAS guidelines adopt as the foundation of prevention.
- Diabetes Prevention Program (United States, NEJM, 2002): 3,234 high-risk people, followed for an average of 2.8 years; the intensive lifestyle intervention (goal of 7% weight loss and at least 150 minutes of physical activity per week) reduced the incidence of diabetes by 58% compared with placebo, versus 31% for metformin (Knowler et al.).
- Finnish Diabetes Prevention Study (Finland, NEJM, 2001): 522 overweight people with impaired glucose tolerance, followed for 3.2 years; individualized advice on weight, dietary fat and physical activity; cumulative incidence of 11% versus 23%, a 58% reduction (Tuomilehto et al.).
The HAS guidelines also cite a 2007 meta-analysis in which regular moderate physical activity, equivalent to 2.5 hours of walking per week, lowered the risk of type 2 diabetes by 30%. The WHO sums it up: a healthy weight, at least 150 minutes of moderate exercise per week, a diet low in sugars and saturated fats, no tobacco: “lifestyle changes are the best way to prevent or delay type 2 diabetes.” Our practical guidelines are in diet and nutrition in prevention, physical activity and the article dedicated to type 2 diabetes prevention.
The benefit lasts as long as the habits last; the annual screening recommended in case of prediabetes is there to check it.
What should you do with your result, together with your doctor?
A blood glucose result is read in its context: fasting conditions, ongoing treatment, recent infection, previous values. A value in the prediabetes range calls for confirmation, not alarm, then a discussion of one or two realistic levers and a check-up after one year. A value at the diabetes threshold calls for a second test and, if it confirms the result, comprehensive care that includes the heart, blood pressure, lipids and kidneys.
What we see in consultation: prediabetes is the moment when efforts pay off the most and are the least demanding. This is the logic of personalized health: spotting a trajectory, choosing the levers that matter for this person, measuring the effect.
Key takeaways
- Prediabetes is a fasting blood glucose above normal without reaching the diabetes threshold (1.26 g/l confirmed on two occasions); it precedes a silent phase of about ten years.
- The HAS recommends a fasting venous blood glucose test for people aged 45 and over with at least one risk factor, repeated every 1 to 3 years, or every year in case of prediabetes; HbA1c is not the screening tool in France.
- Excess weight, sedentary lifestyle, first-degree family history, gestational diabetes and age are the main risk factors.
- NMR metabolomics describes the trajectory (branched-chain amino acids, alanine, lactate, DHA) without establishing a diagnosis.
- Two randomized trials reduced the onset of diabetes by 58% through lifestyle: prediabetes is reversible.
What Sokrate lets you do
The Sokrate service prepares your prevention check-up online with an adaptive self-assessment questionnaire that identifies risk factors for type 2 diabetes, then a doctor writes and signs your Personalized Prevention Plan, which is sent to your regular doctor (médecin traitant) unless you object. As an option, an NMR metabolomic analysis of 249 biomarkers, performed on the Nightingale Health platform, complements blood glucose with the glycolytic profile, amino acids and fatty acids, interpreted by a doctor. A coordination nurse follows up on your goals. Join the waitlist or find out how the pathway works.