Introduction to hyperosmolar hyperglycaemia in adults

Hyperosmolar hyperglycaemia is a medical emergency requiring specialist management. It develops more slowly (over many days) than diabetic ketoacidosis (DKA), which develops within hours. Although uncommon, hyperosmolar hyperglycaemia is under-recognised and has a higher mortality rate than DKA.

Hyperosmolar hyperglycaemia occurs mainly in patients with type 2 diabetes. It usually occurs in older people, but it can present in younger adults and teenagers, in whom it may be the initial presentation of type 2 diabetes.

Hyperosmolar hyperglycaemia is characterised by severe hyperglycaemia, hyperosmolality, dehydration and change in mental state, with little or no ketoacidosis. The disturbance in consciousness varies from minimal drowsiness to comatose, and patients may present with hypovolaemic shock and loss of consciousness in severe cases.

Many patients with diabetes can have severe but transient increases in blood glucose concentration; hyperosmolar hyperglycaemia differs in the duration of hyperglycaemia and the accompanying dehydration. It is distinguished from other hyperglycaemic states (eg DKA) by the patient being unwell and having:

• high effective serum osmolality (often 320 mOsm/kg or more)¹
• extreme hyperglycaemia (usually 30 mmol/L or more)
• severe dehydration.

Patients with hyperosmolar hyperglycaemia usually have no significant ketosis or ketonaemia, though they may have mild acidosis. Some patients present with a mixed picture of both DKA and hyperosmolar hyperglycaemia.