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 NICE NG17,NICE NG18.
• 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 NICE NG17.
• 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 NICE NG17.
• Serum C-peptide: Not routinely measured at initial diagnosis but considered if diabetes classification remains uncertain, especially if autoantibody tests are negative NICE NG17.
• HbA1c measurement: To assess average blood glucose control over 2–3 months and support diagnosis and management planning NICE CKS,NICE CKS.
• Urine albumin:creatinine ratio (ACR): To detect proteinuria as a marker of kidney damage and cardiovascular risk, ideally from a morning urine sample NICE CKS,NICE CKS.
• Serum creatinine and estimated glomerular filtration rate (eGFR): To assess kidney function NICE CKS,NICE CKS.

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