The values below are commonly used reference thresholds found in the medical literature (WHO, Wikipedia). They are provided for general information, not for self-interpretation of test results.

Glycated Hemoglobin (HbA1c)

This test shows the average blood glucose level over roughly the past 2–3 months, since it reflects the proportion of red blood cell hemoglobin that glucose has bound to over the cell's lifespan (3–4 months). It can be taken regardless of food intake.

  • Normal: below 5.7% (<40 mmol/mol)
  • Prediabetes: 5.7–6.4% (40–47 mmol/mol)
  • Diabetes: typically 6.5% or higher (≥48 mmol/mol)

Fasting Plasma Glucose

Measured after at least 8 hours without food.

  • Normal: below 5.6 mmol/L (<100 mg/dL)
  • Prediabetes ("impaired fasting glucose"): by ADA criteria — 5.6–6.9 mmol/L (100–125 mg/dL); by WHO criteria — slightly stricter, 6.1–7.0 mmol/L (110–125 mg/dL)
  • Diabetes: typically 7.0 mmol/L or higher (≥126 mg/dL)

Oral Glucose Tolerance Test (OGTT)

Procedure: a fasting blood sample is taken first, then the person drinks a standardized solution containing 75 g of glucose (different protocols are used for pregnancy screening — 50 g for initial screening and 100 g for confirmation), after which glucose is measured again, most often after 2 hours.

  • Normal (at 2 hours): below 7.8 mmol/L (<140 mg/dL)
  • "Impaired glucose tolerance" (prediabetes): 7.8–11.1 mmol/L (140–200 mg/dL)
  • Diabetes: typically 11.1 mmol/L or higher (≥200 mg/dL)

Random Glucose Measurement

A glucose measurement taken at any time of day, regardless of the last meal. It's usually used together with classic symptoms (thirst, frequent urination, weight loss) rather than as a standalone test. The approximate threshold for diabetes is 11.1 mmol/L (≥200 mg/dL) or higher combined with symptoms.

How the Diagnosis Is Confirmed

If a single test result is borderline and there are no pronounced symptoms or a clearly high glucose level, common practice (per the WHO) is to usually repeat the test on another day to confirm. Fasting glucose testing is often described as the most convenient and simplest to perform compared with the OGTT. Gestational diabetes uses separate, pregnancy-specific criteria — see the "Gestational Diabetes" page for details.

This article presents reference values used in the medical literature and is not a guide for self-interpreting test results or making a diagnosis. Only a doctor can interpret results and order the necessary tests.