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Type 1 is absolute insulin deficiency; type 2 is resistance with relative deficiency
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- Type 1: autoimmune destruction of beta cells, with absolute insulin deficiency. Antibodies to GAD, IA-2 and insulin; associated with HLA-DR3 and DR4. Prone to ketoacidosis because unrestrained lipolysis proceeds
- Type 2: insulin resistance plus progressive beta cell failure. Associated with obesity and inactivity. Ketoacidosis is uncommon, since residual insulin suppresses lipolysis, but hyperosmolar hyperglycaemic state occurs
- MODY: monogenic, autosomal dominant, presenting under 25 with a strong family history and no antibodies or obesity. Some subtypes respond well to sulfonylureas
- LADA: slowly progressive autoimmune diabetes in adults, often misdiagnosed as type 2
- Secondary: pancreatic disease, Cushing syndrome, acromegaly, phaeochromocytoma, steroids, thiazides, antipsychotics
- Gestational: driven by placental anti-insulin hormones
Diagnostic thresholds: fasting glucose 7.0 mmol/l or more, random or 2-hour value 11.1 or more, or HbA1c 48 mmol/mol (6.5 per cent) or more, with symptoms or on two occasions.