Osmolality.

An understanding of the osmotic physiology and colligative properties of a solution will benefit the emergency physician in proper ordering and interpretation of serum osmolality measurements. Though of use in evaluating disorders of water metabolism, the serum osmolality plays a major role in the Emergency Department evaluation of impaired mental status, especially in alcoholics. A significant discrepancy between calculated and measured values may be the earliest laboratory finding in methanol, ethanol, and ethylene glycol ingestion.