Osmolar gap

Osmolar gap refers to the disparity between the measured serum osmolality and the calculated serum osmolality.

Osmolar Gap = Measured Posm – Calculated Posm

The normal osmolar gap is  10-15 mmol/L

Osmolar gap measurement provides a reasonably good screening procedure for toxins. Calculating intoxicants increase measured serum osmolality .

In a patient suspected of poisoning, a high osmolar gap (particularly if ≥ 25) with an otherwise unexplained high anion gap metabolic acidosis is suggestive of either methanol or ethylene glycol intoxication