Osmolal gap

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

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It is typically calculated as: OG = measured serum osmolality - (2 X serum sodium + [[blood sugar|serum glucose]/18] + serum [[urea]/2.8/])

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

See also

• Osmolality
• Metabolic acidosis