Causes of an elevated osmol gap are numerous.

When this is not the case, the term "osmol gap" can be used when units are mixed to provide a clinical estimate.

The osmol gap is typically calculated as:

The calculated osmolality is then subtracted from the measured osmolality to provide the osmol gap, or the difference between these two values.

While it is possible to convert between osmolality and osmolarity, thereby deriving a more mathematically correct osmol gap calculation, in actual clinical practice this is not done.

Because the calculated osmol gap can therefore be a conflation of both terms (depending on how it is derived), neither term (osmolal gap nor osmolar gap) may be semantically correct.

In chemistry, the osmole (Osm or osmol) is a non-SI unit of measurement that defines the number of moles of solute that contribute to the osmotic pressure of a solution.

If, however, the calculated gap is above an acceptable range, then it is an indication that there is something else dissolved in the serum that is producing an osmol gap, which can be a major clue in determining what is ailing the patient.