Osmolal gap

Osmolal gap is the difference between measured serum osmolality and calculated serum osmolality.

It is typically calculated as: OG = measured serum osmolality - (2 X serum sodium + serum glucose + serum urea)

Where:
 * 2 X serum sodium + serum glucose + serum urea = the calculated serum osmolality and all measures are in mmol/L.
 * OG = osmolal gap

In US customary units the calculated osmolarity is: ( 2 x sodium ) + glucose/18 + BUN/2.8.

A normal osmolal gap is < 12 mmol/L.

Causes of an elevated osmolal gap are numerous. Noted causes are:
 * ethanol intoxication
 * methanol ingestion
 * ethylene glycol ingestion