Osmolal gap

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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. Several causes are:

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