Diagnostic criteria for T2DM (HbA1c, fasting glucose, OGTT)?

Clinical answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Diagnostic criteria for type 2 diabetes mellitus can be established through several methods:

An HbA1c level of 48 mmol/mol (6.5%) or above indicates type 2 diabetes and warrants referral for further care .
A diagnosis can also be made based on clinical grounds in adults presenting with hyperglycaemia, with considerations for other diabetes subtypes .
For women with gestational diabetes, a fasting plasma glucose level of 7.0 mmol/litre or above at diagnosis suggests the need for immediate treatment with insulin, with or without metformin, alongside diet and exercise changes .
A fasting plasma glucose level between 6.0 and 6.9 mmol/litre in women with gestational diabetes, particularly if accompanied by complications like macrosomia or hydramnios, may also lead to a consideration for immediate insulin treatment .
While not explicitly detailed for general type 2 diabetes diagnosis in the provided text, an HbA1c level between 39 mmol/mol and 47 mmol/mol (5.7% and 6.4%) indicates a high risk of developing type 2 diabetes .

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