Diabetes Mellitus and Hypoglycemia
Diabetes
Type 1 diabetes is autoimmune beta-cell destruction with insulin deficiency; type 2 involves insulin resistance and relative deficiency, often with obesity and acanthosis nigricans. MODY is monogenic, non-insulin-dependent, and autosomal dominant. Diagnose diabetes with fasting glucose ≥126 mg/dL, random glucose ≥200 mg/dL with symptoms, or HbA1c ≥6.5%. Diabetic ketoacidosis requires dehydration correction, insulin infusion, and careful monitoring for cerebral edema. Trap: HbA1c may be normal early in type 1 and is unreliable in hemoglobinopathies.
Hypoglycemia
In a symptomatic or high-risk infant, obtain a critical sample before treatment: glucose, insulin, C-peptide, beta-hydroxybutyrate, free fatty acids, lactate, ammonia, cortisol, GH, and urine organic acids. Hyperinsulinism shows high insulin, low ketones, low free fatty acids, and high glucose requirement. Glycogen storage disease shows hepatomegaly, lactic acidosis, and ketosis. Fatty acid oxidation defects show hypoketotic hypoglycemia. Ketotic hypoglycemia of childhood is a diagnosis of exclusion.
Worked example
A 2-day-old has glucose 24 mg/dL, high insulin, low beta-hydroxybutyrate, and needs 12 mg/kg/min glucose. This is congenital hyperinsulinism; start IV glucose, obtain critical labs, and seek diazoxide response testing. Never send a hypoglycemic child home without a cause.