HHS remains associated with high short-term mortality, especially in patients with metabolic acidosis in the absence of ketoacidosis. A retrospective cohort study published in Diabetology International evaluated clinical characteristics and outcomes of hospitalized patients with HHS at a university hospital in Japan.

The analysis included 84 consecutive patients diagnosed with HHS between 2018 and 2023. Patients were classified as having isolated HHS or mixed diabetic ketoacidosis and hyperglycemic hyperosmolar syndrome (DKA/HHS) based on established diagnostic criteria. A prespecified subgroup analysis further divided isolated HHS cases according to the presence or absence of metabolic acidosis.

The median age of the cohort was 75 years, highlighting the predominance of HHS in older adults. Infection was identified as the triggering factor in 51.2% of patients. Approximately 70% of individuals were not receiving any diabetes medication at admission, indicating poor baseline glycemic management.

Clinical outcomes differed substantially by HHS phenotype. Thirty-day mortality was significantly higher in the isolated HHS group at 26.0%, whereas no deaths occurred in the mixed DKA/HHS group. Within isolated HHS, the presence of metabolic acidosis was associated with markedly worse prognosis. Thirty-day mortality reached 54.6% in patients with acidosis compared with 20.7% in those without acidosis.

These findings demonstrate that isolated HHS, particularly when accompanied by metabolic acidosis, confers a markedly elevated risk of early mortality. The results emphasize the importance of early biochemical risk stratification and consistent diabetes management to prevent severe hyperosmolar crises in elderly populations.