Hyperglycemic Hypernatremic Hypertonic State: A Predominant HHS Subtype and Its Clinical and Diagnostic Features.

CONTEXT: Hyperglycemic hyperosmolar state (HHS) with concurrent hypernatremia is an emerging and under-investigated subtype of HHS.

OBJECTIVE

To investigate the clinical characteristics, prevalence, and diagnostic parameters of this under-recognized HHS subtype.

METHODS

We conducted a retrospective study of consecutive adults with diabetes admitted with HHS from 2018 to 2024 at a single institution. We assessed the measured and corrected sodium, free water deficit, calculated effective serum osmolarity, calculated total serum osmolarity, and coexisting diabetic ketoacidosis (DKA) and metabolic acidosis.

RESULTS

Among 174 patients with HHS, hypernatremia based on measured sodium (> 145 mmol/L) was uncommon (14/174, 8%), consistent with prior reports. However, hypernatremia based on corrected sodium for hyperglycemia was highly prevalent (166/174; 95.4%), suggesting that HHS with hypernatremia is the predominant subtype of HHS. Effective serum osmolarity > 300 mOsm/L was more sensitive than total serum osmolarity > 320 mOsm/L for diagnosing HHS. Additionally, 65.5% (114/174) of HHS cases had concurrent DKA, suggesting that the traditional exclusion of significant ketonemia and acidemia in HHS diagnosis may warrant reconsideration.

CONCLUSION

HHS with hypernatremia, defined by corrected sodium, is highly prevalent and clinically relevant, as corrected sodium better reflects the true free water deficit. HHS management should include evaluating both measured and corrected sodium, adopting effective serum osmolarity > 300 mOsm/L as a more sensitive diagnostic criterion, and reevaluating the exclusion criteria of significant ketonemia and acidosis. These refinements may enhance diagnostic accuracy and enable more personalized fluid management in HHS.