Clinical reference support
Osmolality calculator
Calculate serum osmolality from sodium, glucose, and BUN in mg/dL. Optionally display raw measured-minus-calculated arithmetic; this tool does not diagnose a cause or direct care.
Scope and limits
- Uses reviewed formula arithmetic and one cited normal serum-osmolality reference interval only.
- Does not identify a toxin, classify a patient, apply an osmolar-gap threshold, choose treatment, or retain results.
- Use the current laboratory method, units, clinical context, and veterinary judgment.
Source and formula
The Merck Veterinary Manual gives: osmolality = 2(Na⁺) + glucose/18 + BUN/2.8, with glucose and BUN in mg/dL, and cites normal serum osmolality as 290–310 mOsm/L. Raw gap, when entered, is measured osmolality minus calculated osmolality; no threshold or interpretation is applied.
Formula audit trail
The formula trail appears after valid values are entered.
Source: Merck Veterinary Manual Fluid Resuscitation Plan in Animals. Reviewed July 2026.