In a 13‑15‑year‑old adolescent with polyuria, polydipsia, fasting plasma glucose 8‑10 mmol/L and HbA1c 7.8%, what is the appropriate next step in evaluation and management?

Diagnosis is Already Confirmed—Start Metformin Immediately

You are correct: this adolescent already meets diagnostic criteria for diabetes with two confirmatory tests (fasting glucose 8-10 mmol/L and HbA1c 7.8%), so starting metformin is the appropriate next step rather than performing additional random glucose testing. 1

Why the Diagnosis is Already Established

The American Diabetes Association criteria for diagnosing diabetes in children require:

• Fasting glucose ≥7.0 mmol/L (126 mg/dL) on two occasions, OR
• HbA1c ≥6.5% (48 mmol/mol), OR
• Random glucose ≥11.1 mmol/L (200 mg/dL) with classic symptoms 1, 2

This patient has:

• Fasting glucose 8-10 mmol/L (well above the 7.0 mmol/L threshold) 1
• HbA1c 7.8% (well above the 6.5% threshold) 1
• Classic symptoms of polyuria and polydipsia 1, 2

When a symptomatic patient has two different diagnostic tests both exceeding thresholds, the diagnosis is confirmed without need for additional testing. 1 A random blood glucose would be redundant and delay treatment unnecessarily.

Critical Safety Assessment Before Starting Metformin

Before initiating metformin, you must rule out:

1. Diabetic Ketoacidosis (DKA)

• Check for ketones in blood or urine immediately 3
• Assess for signs of DKA: nausea, vomiting, abdominal pain, Kussmaul breathing, altered mental status 3
• If ketosis or DKA is present, insulin therapy is required first—metformin is contraindicated in DKA 3, 4

2. Type 1 vs Type 2 Diabetes Differentiation

• The distinction can be difficult in adolescents due to rising obesity rates 1
• Consider checking autoantibodies (GAD65, IAA, IA-2, ZnT8) and C-peptide to differentiate 1
• If type 1 diabetes is suspected (presence of ≥2 autoantibodies, low C-peptide, ketosis), insulin is required, not metformin 3, 1

3. Renal Function

• Check eGFR—metformin requires eGFR >30 mL/min/1.73 m² for safety 3
• Metformin is contraindicated in significant kidney impairment 4

Initiating Metformin Treatment

For metabolically stable adolescents with confirmed type 2 diabetes, start metformin 500 mg once daily with dinner, titrating to a maximum of 2,000 mg daily over 2-4 weeks. 3

Key points about metformin in adolescents:

• FDA-approved for children ages 10-16 years with type 2 diabetes 4
• Take with meals to reduce gastrointestinal side effects (diarrhea, nausea, upset stomach) 4
• Common side effects typically resolve after several weeks on therapy 4
• Avoid excessive alcohol consumption, which increases lactic acidosis risk 4

Monitoring and Treatment Escalation

• Measure HbA1c every 3 months until target <7% is achieved, then every 6 months 3
• If HbA1c remains above target after 3 months on maximum tolerated metformin, add a second agent (SGLT2 inhibitor, GLP-1 receptor agonist, or basal insulin) 3
• For marked hyperglycemia at presentation, consider initiating dual therapy with basal insulin plus metformin immediately 3

Common Pitfall to Avoid

Do not delay treatment by ordering additional confirmatory tests when diagnostic criteria are already met with two different tests in a symptomatic patient. 1 The metabolic state in adolescents can deteriorate rapidly, particularly if this turns out to be type 1 diabetes, with risk of progression to DKA. 1