Hyperosmolar Hyperglycaemic State (HHS) occurs in people with Type 2 diabetes, who may be experiencing very high blood glucose levels (often over 40mmol/l). It can develop over a course of weeks through a combination of illness, dehydration and an inability to take normal diabetes medication due to the effect of illness. Symptoms can include frequent urination and great thirst, nausea, dry skin, disorientation and, in later stages, drowsiness and a gradual loss of consciousness.

It is a potentially life-threatening emergency.

Hospital treatment for HHS involves replacing the lost fluid caused by high glucose levels and the administration of insulin through a vein, to bring the blood glucose down to an acceptable level.

It does not usually lead to the presence of ketones in the urine, as occurs in ketoacidosis, which is why it was previously referred to as HONK (hyperglycaemic hyperosmolar non-ketotic coma). Ketones develop when the blood glucose level is high and a lack of insulin is available to the body, which would normally allow glucose to enter the cells for energy. Because people with Type 2 diabetes may still be producing some insulin, these acidic by-products may not be created.