Prediabetes: How to Detect It Before It Develops into Diabetes

Prediabetes is an intermediate stage between normal blood glucose regulation and type 2 diabetes. Blood glucose levels are already higher than normal but have not yet reached the threshold for a diabetes diagnosis. Prediabetes causes no pain, usually has no symptoms and is detected almost exclusively through blood tests. This is particularly important because, at this stage, dietary changes, losing a few per cent of body weight and regular physical activity can reverse the condition or delay the onset of diabetes for many years. It is estimated that several million adults in Poland have prediabetes, most of whom are unaware of it.

Who should be tested?

The Polish Diabetes Association (Polskie Towarzystwo Diabetologiczne, PTD) recommends diabetes screening every 3 years for everyone over the age of 45, and annually, regardless of age, for people with the following risk factors:

• overweight or obesity (BMI ≥ 25 kg/m² or waist circumference above 80 cm in women and 94 cm in men),
• diabetes in a parent or sibling,
• low levels of physical activity,
• high blood pressure, abnormal blood lipids (low HDL, high triglycerides) or cardiovascular disease,
• a history of gestational diabetes or giving birth to a baby weighing more than 4 kg,
• polycystic ovary syndrome (PCOS),
• previously diagnosed prediabetes,
• obstructive sleep apnoea or the use of medicines that increase blood glucose levels (such as glucocorticoids).

Three tests that establish the diagnosis

Fasting blood glucose

The simplest investigation is a Glucose – laboratory test performed on a venous blood sample collected in the morning after 8–14 hours without food. A result of 70–99 mg/dl (3.9–5.5 mmol/l) is considered normal. A result of 100–125 mg/dl (5.6–6.9 mmol/l) indicates impaired fasting glucose, one form of prediabetes. A result of 126 mg/dl (7.0 mmol/l) or higher, confirmed by a second measurement on another day, indicates diabetes. A home blood glucose meter cannot be used to establish a diagnosis; only laboratory measurement of glucose in venous blood plasma is suitable.

Oral glucose tolerance test (OGTT)

This test is performed when fasting blood glucose is abnormal or borderline, and is also routinely used during pregnancy. After an initial fasting blood sample, the patient drinks a solution containing 75 g of glucose. Another blood sample is collected after 120 minutes. The 2-hour result is interpreted as follows: below 140 mg/dl (7.8 mmol/l) is normal; 140–199 mg/dl (7.8–11.0 mmol/l) indicates impaired glucose tolerance (another form of prediabetes); and 200 mg/dl (11.1 mmol/l) or higher indicates diabetes. During the test, you should remain seated and relaxed, without eating, smoking or drinking coffee. In the days leading up to the test, maintain your usual diet without restricting carbohydrates, as carbohydrate restriction can distort the results.

Glycated haemoglobin (HbA1c)

Glycated haemoglobin (HbA1c) reflects average blood glucose levels over approximately the previous 3 months and does not require fasting. Values of 5.7–6.4% indicate prediabetes, while 6.5% or higher indicates diabetes. HbA1c may be falsely low in some forms of anaemia and following blood loss, and falsely elevated in iron deficiency. It should therefore be interpreted alongside a full blood count. Testing must be performed using a certified method, which is standard practice in major laboratories.

Additional laboratory tests

Fasting Insulin – laboratory test and the HOMA-IR index can be used to assess insulin resistance, which often develops years before prediabetes. They are not used to diagnose diabetes but may help explain the underlying mechanism and motivate lifestyle changes. Lipid profile (cholesterol) – laboratory test is important because abnormal glucose and lipid metabolism frequently occur together and jointly increase the risk of a heart attack. Creatinine – laboratory test with eGFR and Urinalysis (albuminuria) assess kidney health, as diabetes can cause kidney damage without obvious symptoms. Alanine aminotransferase (ALT) – laboratory test and Gamma-glutamyl transferase (GGT) – laboratory test help identify fatty liver disease, which is present in many people with insulin resistance. Thyroid-stimulating hormone (TSH) – laboratory test helps exclude hypothyroidism as a possible cause of weight gain. Vitamin B12 – laboratory test is important for people already taking metformin, which can reduce vitamin B12 absorption.

What to do with your results

A diagnosis of prediabetes is not a sentence to developing diabetes, but it is a signal to take action and arrange regular monitoring. The interventions supported by the strongest evidence include:

• Losing 5–7% of body weight if you are overweight: major clinical trials have shown that this can reduce the risk of progression to diabetes by more than half.
• Physical activity for at least 150 minutes per week at moderate intensity (brisk walking, cycling or swimming), ideally combined with strength training, which improves muscle sensitivity to insulin.
• A healthy diet based on vegetables, whole grains, pulses, fish and plant-based fats, while limiting added sugars, sugary drinks and highly processed foods. The Mediterranean diet has the strongest supporting evidence.
• Sleep and stress management: chronic sleep deprivation and elevated cortisol levels can worsen blood glucose regulation independently of diet.
• Metformin may be considered by a doctor for people at particularly high risk, especially those with a BMI ≥ 35, those under 60 or those with a history of gestational diabetes.

Blood glucose monitoring (fasting glucose or HbA1c) should be repeated every 6–12 months. Lipid profiles, blood pressure checks and body weight monitoring should form part of the same routine. Your doctor should interpret the results and make treatment decisions; this article is intended to help you understand the subject before your appointment.

Preparing for blood glucose tests

Fasting means going without food or drinks other than water for 8–14 hours, and avoiding chewing gum and cigarettes on the morning of the test. Maintain your normal diet for the previous 3 days, including at least 150 g of carbohydrates daily. Testing should not be performed during an infection, immediately after surgery or following a sleepless night, as stress and inflammation can increase blood glucose levels. Regular medicines should be taken according to your doctor’s instructions; glucocorticoids and certain diuretics can increase glucose results.

Undiagnosed hyperglycaemia is sometimes only discovered after a complication develops, such as a wound on the foot or lower leg that fails to heal for weeks. Fasting Glucose – laboratory test and Glycated haemoglobin (HbA1c) are the first-line investigations in such cases. Find out more in our article A wound that won’t heal: causes, tests and when to visit a wound care clinic.

Frequently asked questions

Does prediabetes always progress to diabetes?

No. Without intervention, a substantial proportion of people develop diabetes within 5–10 years, but lifestyle changes can restore normal blood glucose regulation in many cases.

Which test is best: fasting glucose, OGTT or HbA1c?

These tests complement one another. Fasting Glucose – laboratory test is the least expensive and is sufficient for initial screening. OGTT can detect impaired glucose tolerance that is not apparent in fasting results. Glycated haemoglobin (HbA1c) reflects average blood glucose over approximately 3 months and does not require fasting.

Do I need a referral?

No. Glucose – laboratory test, Glycated haemoglobin (HbA1c), Insulin – laboratory test and OGTT can be purchased online and performed at a blood collection centre. Allow approximately 2.5 hours for an OGTT appointment.

Sources

• Polish Diabetes Association, Clinical Guidelines for the Management of People with Diabetes 2025, 2025. ptdiab.pl
• Polish Diabetes Association, PTD Guidelines, 2023-2026 editions, 2026. ptdiab.pl
• American Diabetes Association, Diabetes Care, Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2025, 2025. doi.org