Diabetes: hyperglycaemia found (confirm, classify, spot the emergency)

In the practice, straight away

• Urine dipstick (glucose, ketones) and capillary blood glucose
• Child or adolescent with suspected diabetes: refer the same day to a paediatric diabetes team, without waiting for laboratory tests.
• Adult with ketosis, vomiting, abdominal pain, rapid breathing or altered consciousness: emergency department (possible ketoacidosis).

Fasting laboratory tests (overnight fast of 10 to 12 hours; at least 8 hours without calorie intake)

• Confirmatory fasting venous plasma glucose
• HbA1c (second test, on the same sample or later)if neededTo confirm with a different test: two different abnormal tests (fasting plasma glucose and HbA1c), on the same day or on two dates, confirm the diagnosis ^[2]. Not reimbursed at diagnosis ^[11].
• Oral glucose tolerance test (75 g glucose, fasting and 2-hour plasma glucose)if needednon-French guidelineBorderline fasting plasma glucose and strong clinical suspicion, or HbA1c abnormality (haemoglobinopathy, pregnancy, altered red cell turnover): OGTT is a diagnostic criterion; ensure at least 150 g of carbohydrate a day during the previous 3 days ^[2].

Fasting laboratory tests

• HbA1c (baseline value to set the target)
• FBC (including platelets, for the FIB-4 score)
• Lipid profile
• Liver function tests: AST
• ALT
• GGT
• Alkaline phosphatase
• PT (to calculate the FIB-4 score)
• Serum creatinine with eGFR
• Anti-GAD antibodies (if features of type 1 diabetes)if needednon-French guidelineAdult with features of type 1 diabetes: age at diagnosis < 35 years, BMI < 25 kg/m², involuntary weight loss, ketosis, plasma glucose > 3.6 g/L (20 mmol/L) at diagnosis, rapid need for insulin ^[2]; to be measured early, when the false-negative rate is lowest ^[5].
• Anti-IA2 antibodies (if anti-GAD negative and persistent doubt)if needednon-French guidelineNegative anti-GAD while type 1 diabetes is still suspected: anti-IA2 (or anti-ZnT8) are the second step ^[2]; two different antibodies reduce false negatives ^[5].
• C-peptide with simultaneous plasma glucose (patient already on insulin, uncertain classification)if needednon-French guidelineOnly in a patient treated with insulin whose type remains uncertain, preferably at a distance from diagnosis: a non-fasting sample within 5 hours of a meal is enough ^[2,5].

Urine tests

• Urine albumin:creatinine ratio (spot sample)