Hyperosmolar Hyperglycaemic State (HHS)
In hyperosmolar hyperglycaemic state (HHS), residual insulin suppresses ketone production but not hyperglycaemia, so days of osmotic diuresis produce extreme dehydration and hyperosmolality rather than acidosis.
Definition
Hyperosmolar hyperglycaemic state requires hypovolaemia, marked hyperglycaemia and a high measured or calculated serum osmolality without significant ketosis or acidosis. Glucose is usually 30 mmol/L or above and osmolality 320 mOsm/kg or above, with ketones 3.0 mmol/L or below, pH 7.3 or above and bicarbonate 15.0 mmol/L or above. No precise definition is agreed, and HHS must not be diagnosed on biochemistry alone.
First principles
Residual insulin blocks ketosis but not hyperglycaemia
HHS almost always occurs in type 2 diabetes. Enough insulin remains to suppress lipolysis and hepatic ketogenesis, but not enough to control glucose during illness or an interruption in treatment. That single fact separates HHS from DKA. A mixed picture is common, and marked hypovolaemia and hyperosmolality with pH below 7.3 and ketones above 3.0 mmol/L is treated on the DKA pathway.
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