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Comment & Response
August 2016

Toxic Alcohol Calculations and Misinterpretation of Laboratory Results

Author Affiliations
  • 1Ontario Poison Centre, Toronto, Ontario, Canada
  • 2Division of Clinical Pharmacology & Toxicology, Department of Medicine, University of Toronto, Toronto, Ontario, Canada
  • 3Department of Emergency Medicine, Queen’s University, Kingston, Canada
  • 4Department of Biomedical & Molecular Science, Queen’s University, Kingston, Canada
JAMA Intern Med. 2016;176(8):1227-1228. doi:10.1001/jamainternmed.2016.3714

To the Editor We read with interest the Teachable Moment in a recent issue of JAMA Internal Medicine by Himmel and colleagues1 and commend them on sharing this experience of medical error and disclosure. Regarding the clinical aspects of toxic alcohol poisoning, a few points merit discussion.

First, the ethanol concentrations provided are discordant. The molecular mass of ethanol is 46.1 g/mol and to convert mmol/L to mg/dL, multiply by 4.61 (this corrects for the unit change); therefore a level of 8.1 mmol/L converts to 37.3 mg/dL, not 144 mg/dL (31.2 mmol/L). Depending on which is correct, very different interpretations will be drawn. Second, when facing an elevated osmole gap, one must determine if the gap can be accounted for by ethanol alone. The authors do not specify whether the osmole gap of 27 was adjusted for the ethanol. Importantly, ethanol’s contribution to the osmole gap is more than 1 mosm to 1 mmol. In fact, it ranges from 1.21 to 1.25 mosm to 1 mmol.2,3 Practically speaking, a conservative correction of 1.20 (ie, adding a fifth of ethanol) becomes particularly important at high concentrations of ethanol, say over 20 mmol/L, a common source of high osmole gap confusion and unnecessary fomepizole administration.3 Only if the level is 8.1 mmol/L, rather than 31.3 mmol/L, is it justified to test for toxic alcohol levels.

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