What are the key biochemical markers for diagnosing diabetes mellitus in primary care?

Key biochemical markers used for diagnosing diabetes mellitus in primary care include:

• Glycated haemoglobin (HbA1c) level of 48 mmol/mol (6.5%) or above is diagnostic for type 2 diabetes in adults who are not pregnant.
• Random venous plasma glucose concentration ≥11.1 mmol/litre is diagnostic.
• Fasting venous plasma glucose concentration ≥7.0 mmol/litre is diagnostic.
• Two-hour venous plasma glucose concentration ≥11.1 mmol/litre after a 75 g oral glucose tolerance test (OGTT) is diagnostic.
• In suspected type 1 diabetes, diagnosis is primarily clinical but supported by plasma glucose measurements; diabetes-specific autoantibodies can be measured to confirm type 1 diabetes.
• Serum C-peptide measurement is not routinely used at initial diagnosis but may be considered if classification is uncertain.

These markers are used in accordance with WHO criteria and NICE guidelines for diagnosis and classification of diabetes mellitus in primary care settings.

References: ¹,²,⁴