How are prediabetes and diabetes diagnosed?

To diagnose diabetes or prediabetes, your doctor can choose from the following tests to measure the amount of glucose in your blood:


  • Fasting plasma glucose: a blood test to measure your blood glucose after 8 hours of fasting.

  • Oral glucose tolerance test: measuring blood glucose while fasted and 2 hours after taking 75 g of glucose.

  • Haemoglobin A1c: a measure of the amount of glycated haemoglobin in your blood. Haemoglobin A1c indicates how much glucose you have had in your blood in the preceding 3 months.

For these blood glucose tests, your results may fall in the ‘normal’, ‘prediabetes’ or ‘diabetes’ ranges as shown:

For fasting plasma glucose,


  • glucose equal to or less than 6.0 mmol/L or less than 110 mg/dL is normal;

  • glucose range between 6.1 mmol/L and 6.9 mmol/L or between 110 mg/dL and less than 126 mg/dL is considered prediabetic;

  • glucose equal to or greater than 7 mmol/L or 126 mg/dL on two separate tests indicates you have diabetes.

For 2-hour plasma glucose after an oral glucose tolerance test,


  • glucose less than 7.8 mmol/L or 140 mg/dL is normal;

  • glucose reading between 7.8 mmol/L and 11.0 mmol/L or between 140 mg/dL and less than 200 mg/dL indicates prediabetes;

  • glucose equal to or greater than 11.1 mmol/L or 200 mg/dL indicates that you have diabetes.


For Haemoglobin A1c,


  • a range between 4% and 5.6% is normal;

  • a range between 5.7% and 6.5% is considered prediabetic;

  • a value higher than 6.5% means that you have diabetes.