Laboratory

Calculated Serum Osmolality

Name: Calculated Serum Osmolality | StudyPrometric Tools
Keywords: osmolality, osmolar, sodium, glucose, bun, laboratory

Calculates expected serum osmolality from basic metabolic panel.

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Parameters

Calculated Serum Osmolality Result

FormulaCalculated Osmolality = (2 × Na) + (Glucose / 18) + (BUN / 2.8)

Clinical Pearls

True hyponatremia is hypo-osmolar (Calculated Osm < 275). If hyponatremia is present with a normal or high calculated osmolality, it suggests pseudohyponatremia (e.g., from severe hyperglycemia or hyperlipidemia).