Prediabetes: Symptoms, Causes, Diagnosis and Prevention

Prediabetes describes a state in which blood glucose is higher than normal but does not yet meet the diagnostic criteria for diabetes. It is not the same as type 2 diabetes, and having prediabetes does not mean diabetes will inevitably develop.

Even so, the result is an important warning: the body may be finding it harder to keep glucose within the normal range.

Many people with prediabetes feel entirely well. The condition is often discovered incidentally — during a routine check-up, a scheduled blood test, or an investigation for something else.

Detecting it early makes it possible to review diet, physical activity, body weight, sleep, blood pressure, cholesterol, and other factors before glucose rises further. Research shows that structured lifestyle change can delay or prevent type 2 diabetes in many people at high risk.

What happens in the body?

Glucose is an important source of energy. After food is digested, it enters the bloodstream. The hormone insulin helps glucose move from the blood into cells, where it is used or stored.

In many people with prediabetes, body tissues gradually become less sensitive to insulin. This is called insulin resistance. The pancreas compensates at first by producing more insulin. Over time that compensation may become insufficient, and glucose levels begin to rise.

The process unfolds differently in different people. In some, fasting glucose rises first. In others, the response after eating or after a glucose load is more clearly affected. In others still, HbA1c is the first measure to change.

Prediabetes and insulin resistance are related but are not the same thing. Insulin resistance can exist before standard tests reach the prediabetes range.

How common is prediabetes?

Global prevalence is difficult to estimate precisely, because different health systems use different tests and thresholds. Instead of the word "prediabetes," the terms impaired fasting glucose and impaired glucose tolerance may be used.

According to the International Diabetes Federation's 2025 estimate, around 635 million adults aged 20–79 have impaired glucose tolerance, and approximately 488 million have impaired fasting glucose. These groups partly overlap, so the figures cannot be added together.

According to the United States Centers for Disease Control and Prevention, more than two in five American adults have prediabetes, and eight in ten of them do not know it. These data cannot be transferred automatically to other countries, but they show how often the condition goes undetected.

Are there symptoms?

Usually there are none.

A person may have raised readings for years without noticing any change in how they feel. Prediabetes therefore cannot be identified by symptoms alone.

The following symptoms may appear once glucose has approached or entered the diabetes range:

• intense thirst;
• frequent urination;
• unexplained weight loss;
• unusual fatigue;
• blurred vision;
• slow wound healing;
• recurrent infections.

These signs do not confirm diabetes, but they do call for medical review and laboratory testing.

Darkening and thickening of the skin on the neck, in the armpits, or in the groin may be linked to insulin resistance. This sign is called acanthosis nigricans, but on its own it does not confirm prediabetes.

Who is at higher risk?

Prediabetes can occur in people of any age and build. Excess weight is an important factor, but not the only one.

Risk may be higher in the presence of:

• type 2 diabetes in a parent or sibling;
• overweight, obesity, or marked abdominal fat;
• low physical activity;
• previous gestational diabetes;
• polycystic ovary syndrome;
• raised blood pressure;
• high triglycerides or low HDL cholesterol;
• cardiovascular disease;
• metabolic dysfunction–associated steatotic liver disease;
• other signs of insulin resistance;
• older age.

The American Diabetes Association recommends considering routine screening from age 35, and earlier where there is excess weight together with additional risk factors. National guidelines may differ.

Some medications, including systemic corticosteroids, certain antipsychotics, and some HIV treatments, can affect glucose levels. Prescribed treatment must never be stopped independently. The question should be discussed with the treating doctor.

How is prediabetes diagnosed?

Diagnosis rests on laboratory blood tests. Symptoms, a home glucose meter, a smartwatch, or a single continuous-monitoring reading cannot confirm prediabetes on their own.

The main tests are:

Test

Prediabetes range under American Diabetes Association criteria

HbA1c (glycated haemoglobin)

5.7–6.4%, or 39–47 mmol/mol

Fasting plasma glucose

100–125 mg/dL, or 5.6–6.9 mmol/L

Glucose 2 hours after a 75 g load

140–199 mg/dL, or 7.8–11.0 mmol/L

HbA1c approximately reflects average glucose over the previous two to three months. The fasting test shows glucose after an overnight period without food. The oral glucose tolerance test assesses the body's response to a standard glucose solution.

Why do the thresholds differ?

There is no single international definition.

The American Diabetes Association uses a fasting range of 100–125 mg/dL. The World Health Organization defines impaired fasting glucose from 110 to 125 mg/dL. The United Kingdom's National Institute for Health and Care Excellence classifies fasting glucose of 5.5–6.9 mmol/L, or HbA1c of 6.0–6.4%, as high risk.

The same result can therefore be classified differently depending on the country and the guideline applied. A doctor considers not only the number but also the medical history, risk factors, symptoms, and the characteristics of the laboratory method used.

Should the test be repeated?

Results can be affected by biological and laboratory variation. If an unexpected raised reading is found in someone without symptoms, the doctor may repeat the test or order another recognised test.

Where results disagree, the test that showed the elevation is repeated. Borderline values are sometimes rechecked after three to six months.

When can HbA1c be unreliable?

HbA1c may be less reliable in certain types of anaemia, in haemoglobin variants, after recent significant blood loss or transfusion, in pregnancy, during dialysis, and with erythropoietin treatment.

In these situations a doctor may rely more on plasma glucose measurements.

Can the condition improve?

Yes. In some people, readings return to the normal range. In others, progression to type 2 diabetes is delayed by years.

The outcome cannot be guaranteed, however. A single normal result also does not mean that lifetime risk has disappeared entirely.

It is more accurate to speak of improved glucose regulation and reduced risk of type 2 diabetes than to promise permanent "cure" or "reversal."

In the Diabetes Prevention Program, structured lifestyle change reduced the relative incidence of type 2 diabetes by 58% over roughly three years compared with placebo. Metformin reduced it by 31%. The participants were at high risk, so the same result is not guaranteed for every patient.

Main approaches to managing prediabetes

Structured lifestyle change

The strongest evidence relates not to short detoxes or extreme diets, but to sustainable change.

In that programme, the targets were at least 150 minutes of moderate physical activity per week and a weight reduction of about 7% in participants who were overweight. Current guidelines use similar reference points, adapted to the individual.

A plan may include:

• regular walking, swimming, cycling, or other aerobic activity;
• strength training appropriate to the person's health;
• reducing long periods of uninterrupted sitting;
• more vegetables and fibre-containing foods;
• suitable protein sources;
• predominantly minimally processed carbohydrate foods;
• fewer sugary drinks and less frequent use of heavily processed foods;
• better sleep;
• stopping smoking;
• monitoring blood pressure and cholesterol.

There is no single mandatory "prediabetes diet." Advice should take into account culture, financial circumstances, coexisting conditions, and food preferences.

Weight loss is not needed by everyone. The decision depends on starting weight, body composition, overall health, and the risk of undernutrition.

Medication

Not everyone needs medication.

Current American Diabetes Association standards allow metformin to be considered in adults at particularly high risk — in particular those aged 25–59 with a body mass index of at least 35 kg/m², higher fasting glucose, HbA1c of 6.0% or above, or previous gestational diabetes. Periodic assessment of vitamin B12 may be needed with long-term metformin use.

The decision depends on kidney function, pregnancy planning, other conditions, side effects, and patient preference.

Treating obesity, hypertension, cholesterol disorders, polycystic ovary syndrome, fatty liver disease, or sleep apnoea may also form part of the overall strategy.

Which specialists may be involved?

Follow-up is often led by a family doctor, general practitioner, or internal medicine specialist.

In particular cases the following may be involved:

• an endocrinologist;
• a registered dietitian;
• an obesity medicine specialist;
• an obstetrician-gynaecologist;
• a paediatrician or paediatric endocrinologist;
• a cardiologist;
• a hepatologist;
• a sleep medicine specialist.

A young or lean person with rapidly rising glucose, weight loss, or pronounced symptoms may need assessment for type 1 diabetes or monogenic forms of diabetes.

How often should tests be repeated?

Where prediabetes is confirmed, tests are usually repeated at least once a year. A check after three to six months may be needed if the reading is close to the diabetes range, symptoms appear, treatment changes, pregnancy is planned, or risk is particularly high.

Monitoring may also cover:

• blood pressure;
• cholesterol and triglycerides;
• body weight or waist circumference;
• liver function;
• physical activity;
• diet and sleep;
• a review of current medications;
• cardiovascular risk assessment.

Daily glucose meter readings or continuous monitoring are not needed by everyone. Continuous glucose monitoring is not yet an established method for diagnosing prediabetes.

When is urgent care needed?

Uncomplicated prediabetes on its own does not usually cause an emergency.

Urgent care is needed in the case of:

• persistent vomiting;
• severe abdominal pain;
• rapid or deep breathing;
• a fruity smell on the breath;
• marked dehydration;
• confusion;
• extreme drowsiness;
• fainting or loss of consciousness.

These signs are not typical of ordinary prediabetes. They may indicate diabetic ketoacidosis or another serious condition.

Persistent thirst, frequent urination, blurred vision, or unexplained weight loss warrant prompt medical review, even if the situation does not appear urgent.

Questions for your doctor

1. Which test showed the prediabetes range?
2. Does the result need to be repeated or confirmed?
3. Which clinical guideline is being used?
4. How close is my reading to the diabetes range?
5. Do I have other metabolic or cardiovascular risks?
6. Should cholesterol, blood pressure, liver, or sleep apnoea be checked?
7. What physical activity is safe for me?
8. Would a dietitian consultation help?
9. Should medication be considered?
10. When should the test be repeated?
11. Could my medications or conditions affect the result?
12. Which symptoms should bring me back sooner?

Common misconceptions

"Prediabetes is just a mild form of diabetes." It is a separate range of increased risk, not the same diagnosis.

"If there are no symptoms, glucose is normal." Most people have no symptoms.

"The only cause is sugary food." Risk is shaped by a combination of genetics, insulin sensitivity, pancreatic function, age, activity, and other factors.

"Prediabetes only happens with obesity." It can develop at a range of body weights.

"One reading from a home meter confirms the diagnosis." Diagnosis requires a laboratory test and medical interpretation.

"Prediabetes always progresses to diabetes." No. The condition may stay stable, improve, or progress.

Frequently asked questions

Is prediabetes considered a disease?

Terminology varies. Some organisations call it a health condition, while the World Health Organization uses the categories of impaired fasting glucose and impaired glucose tolerance. Either way, the result warrants attention and follow-up.

Can a lean person have prediabetes?

Yes. Glucose levels are influenced not only by body weight but also by genetics, age, fat distribution, muscle mass, medication, and pancreatic function.

Does an HbA1c of 5.7% always mean prediabetes?

That is the lower boundary under American Diabetes Association criteria, but not all international guidelines use that threshold. The result should be interpreted by a doctor.

Does walking after meals help?

Light or moderate activity after eating may reduce the post-meal glucose rise in some people. It forms part of an overall plan, but does not replace assessment and treatment.

Do carbohydrates need to be cut out entirely?

Usually not. Quality, quantity, and the composition of the meal matter. Extreme restriction is not suitable for everyone.

Does everyone need metformin?

No. It is considered mainly where the risk of progression is higher.

Can prediabetes return after a normal result?

Yes. If risk factors change, readings may rise again.

Do these criteria apply during pregnancy?

No. Separate diagnostic pathways apply to gestational diabetes and to glucose disorders in pregnancy.

Medical disclaimer

This material is intended for general medical education. It is not a diagnosis, individual consultation, or treatment recommendation.

Symptoms and test results should be interpreted by a qualified healthcare professional, taking into account medical history, medication, examination, and local clinical guidelines.

Adamiani is an international healthcare coordination platform. Adamiani does not replace doctors, clinics, diagnostic services, or emergency care.

AI organizes information. Doctors make medical decisions.

Sources

1. American Diabetes Association — Standards of Care in Diabetes: Diagnosis and Classification of Diabetes. https://diabetesjournals.org/care
2. American Diabetes Association — Prevention or Delay of Diabetes and Associated Comorbidities. https://diabetesjournals.org/care
3. World Health Organization — Diabetes fact sheet. https://www.who.int/news-room/fact-sheets/detail/diabetes
4. National Institute for Health and Care Excellence — Type 2 diabetes: prevention in people at high risk (PH38). https://www.nice.org.uk/guidance/ph38
5. Centers for Disease Control and Prevention — Prediabetes statistics. https://www.cdc.gov/diabetes/communication-resources/prediabetes-statistics.html
6. National Institute of Diabetes and Digestive and Kidney Diseases — Insulin Resistance and Prediabetes. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance
7. International Diabetes Federation — IDF Diabetes Atlas, 11th edition, 2025. https://diabetesatlas.org
8. Diabetes Prevention Program Research Group — Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. New England Journal of Medicine, 2002. https://www.nejm.org/doi/full/10.1056/NEJMoa012512

Internal links

Published article

• Does a 10-Minute Walk After Meals Help Control Blood Sugar?

Planned articles

• What is type 2 diabetes?
• Insulin resistance explained simply
• The HbA1c test
• Blood sugar levels
• Metabolic syndrome
• Fatty liver disease
• Obesity and metabolic health
• Polycystic ovary syndrome and insulin resistance