How do you diagnose diabetes and prediabetes?

By testing your blood glucose (sugar) and HbA1C levels. The haemoglobin A1C test (HbA1C) measures your average blood sugar level over the last 3 months. This test doesn’t require fasting and can be done any time.

Blood glucose in prediabetes and diabetes

Normal human blood sugar = 4-6 mmol/L
Prediabetes is diagnosed if your random blood sugar = 7-11 mmol/L (twice)
Diabetes is diagnosed if you have a random blood sugar > 11 mmol/L (or a fasting blood sugar > 7 mmol/L) (twice).

HbA1C in prediabetes and diabetes

Normal HbA1c = 20-42 mmol/mol (or 4-6%)
Prediabetes is diagnosed if your HbA1c = 42-47 mmol/L (6-6.5%) (twice)
Diabetes is diagnosed if your HbA1c = 48 mmol/mol or over (>6.5%).

HbA1C mmol/mol and %

Confusingly HbA1c comes in 2 different units (% is the older unit). These are the equivalent values.

42 mmol/mol = 6.0% = prediabetes
48 = 6.5 = diabetes
53 = 7
59 = 7.5
64 = 8
75 = 9.

Diabetes UK has a converter to convert HbA1C from mmol/mol to %, and vice versa.

Monitoring of DM in adults (and target HbA1Cs)

Type 1 target values: 48 mmol/mol or lower
Type 2 target values: 48 mmol/mol – 57 mmol/mol.

Summary

We have described how do you diagnose diabetes and prediabetes. We have also given normal blood glucose (sugar) and HbA1C levels. We hope it has been helpful.

Other resource

Here is more information on blood glucose, HbA1c and definitions of DM.

Last Reviewed on 3 April 2024