Estimating toxic alcohol concentration in mg/dL from increase in osmolal gap

The plasma osmolal gap estimates the molar quantity of uncharged molecules and increases only in the presence of the parent alcohol (first column) and not the toxic acid metabolites (eg, formate, glycolate). As a result, the plasma osmolal gap is insensitive in late presentations, since most of the parent alcohol has already been metabolized. The plasma osmolal gap is not sufficiently sensitive to exclude a small ingestion or traces of remaining parent alcohol. The plasma osmolal gap cannot distinguish between the toxic alcohols; thus, clinical suspicion is needed to determine which calculation to apply. The same calculations can be used to convert measured parent alcohol concentrations expressed in mmol/L to mg/dL.