What are the recommended initial investigations for a patient presenting with hyperglycaemia in primary care?

For a patient presenting with hyperglycaemia in primary care, the recommended initial investigations include:

• Confirming hyperglycaemia diagnosis: Measure blood glucose levels, preferably plasma glucose, as patient-held glucose meters are calibrated to plasma glucose equivalents ¹,².
• Assess diabetes subtype: In adults, make an initial clinical diagnosis of type 1 diabetes considering features such as ketosis, rapid weight loss, age under 50 years, BMI below 25 kg/m2, and personal or family history of autoimmune disease, but do not rely on age or BMI alone ¹.
• Diabetes-specific autoantibodies: Measure diabetes-specific autoantibodies in adults with suspected type 1 diabetes at initial diagnosis to support classification, ideally quantitative tests for at least two different autoantibodies ¹.
• Serum C-peptide: Do not routinely measure serum C-peptide at initial diagnosis; consider it only if autoantibody results are negative and diabetes classification remains uncertain ¹.
• HbA1c measurement: Measure HbA1c to assess average blood glucose control over the preceding 2–3 months and to support diagnosis and management planning ⁵,⁶.
• Urine albumin:creatinine ratio (ACR) and serum creatinine: Assess kidney function and detect proteinuria as part of baseline evaluation, especially in type 1 diabetes, to identify risk of diabetic kidney disease ⁵,⁶.