Endocrinology

Hyperosmolar Hyperglycemic State (HHS) & Osmolality Evaluator

Calculates effective osmolality, corrected sodium, free water deficit, and HHS vs DKA diagnostic criteria.

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Parameters

Hyperosmolar Hyperglycemic State (HHS) & Osmolality Evaluator Result

Formula

Effective Osmolality (mOsm/kg) = (2 × Na) + (Glucose / 18)
Total Osmolality = (2 × Na) + (Glucose / 18) + (BUN / 2.8)
Corrected Na = Na + 0.016 × (Glucose - 100)
Water Deficit (L) = TBW × ([Corrected Na / 140] - 1)

Clinical Pearls

Critical diagnostic tool distinguishing between pure HHS (high mortality, extreme dehydration, minimal acidosis) vs DKA in acute emergency admissions.

Limitations

BUN is excluded from effective osmolality calculations because urea freely permeates cell membranes and does not create an effective osmotic gradient across the blood-brain barrier.