A 17-year-old boy with a past medical history of substance abuse (marijuana and alcohol) was presented to the emergency department with extreme agitation and suicidal statements. His mother claimed he consumed 4 glasses of hard liquor with caffeine shortly before presenting to the hospital. His urine toxicology screen was negative for amphetamines, barbiturates, benzodiazepines, cocaine, opiates, and tricyclic antidepressants. However, his urine toxicology screen was positive for cannabinoids. Other laboratory results are shown in Table 1.
Serum analytes.
Questions
What is the calculated osmolal gap with and without including ethanol?
What compounds cause an increase in osmolal gap?
What might explain the discrepant osmolal gap?
Answers
The major osmotic substances in serum are sodium (Na), chlorine, bicarbonate, glucose, and urea. Ethanol is osmotically active and contributes to the serum osmolality in an individual who has been drinking. These analytes are used to calculate serum osmolality from the following equation (1):
Osmolal gap represents the difference between the calculated osmolality and the measured osmolality:
The osmolal gap with and without ethanol is −45 and 0 mOsm/kg, respectively. A negative anion gap virtually always indicates an analytical problem. When ethanol (or methanol, acetone, isopropanol, or ethylene glycol) is present, an increased osmolal gap (>10 mOsm/kg) should be seen (1). In this case, the osmolality was ordered as an add-on test, and the ethanol had presumably volatilized. When comparing calculated and measured osmolality, one must use the same specimen with measurements done at the same time.
Footnotes
Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 4 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; (c) final approval of the published article; and (d) agreement to be accountable for all aspects of the article thus ensuring that questions related to the accuracy or integrity of any part of the article are appropriately investigated and resolved.
M. Kellogg, administrative support, provision of study material or patients.
Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
- Received for publication June 18, 2018.
- Accepted for publication July 20, 2018.
- © 2018 American Association for Clinical Chemistry
Reference
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