Utility of the serum osmol gap in the diagnosis of methanol or ethylene glycol ingestion.

Ingestion of methanol or ethylene glycol is a toxicologic emergency. The osmolal gap has been widely advocated as a screen for serum methanol or ethylene glycol. Unfortunately, for several reasons the osmolal gap fails in this capacity. First, an accurate serum osmolality can often not be obtained. Second, the calculated serum osmolarity will vary greatly, depending on the formula used to estimate it. Third, ethylene glycol has such a large molecular weight that even toxic amounts may contribute minimally to a patient's overall osmolality. Finally, because of metabolism, little ethylene glycol or methanol may be present when a patient presents with toxicity. These limitations invalidate the osmolal gap as a screen for ethylene glycol or methanol ingestion.