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 considering features such as ketosis, rapid weight loss, age of onset under 50 years, BMI below 25 kg/m2, and personal or family history of autoimmune disease ¹.
• Diabetes-specific autoantibodies: Measure these in adults with an initial diagnosis of type 1 diabetes to support classification, ideally quantitative tests for at least two different autoantibodies ¹.
• Serum C-peptide: Not routinely measured at initial diagnosis but considered if diabetes classification remains uncertain, especially if autoantibody tests are negative ¹.
• HbA1c measurement: To assess average blood glucose control over 2–3 months and support diagnosis and management planning ⁵,⁶.
• Urine albumin:creatinine ratio (ACR): To detect proteinuria as a marker of kidney damage and cardiovascular risk, ideally from a morning urine sample ⁵,⁶.
• Serum creatinine and estimated glomerular filtration rate (eGFR): To assess kidney function ⁵,⁶.

These investigations help confirm the diagnosis, classify the diabetes type, and identify early complications or associated risks to guide management in primary care.