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MBBS QUESTION #10376
Question 1
The osmolar gap (measured serum osmolality minus calculated osmolality) becomes markedly elevated in poisoning with which class of substances, an important diagnostic clue in an unresponsive patient with unexplained metabolic acidosis?
  • Osmotically active, small, unmeasured molecules such as methanol, ethylene glycol, or isopropyl alcohol✔️
  • Sodium chloride excess alone
  • Simple dehydration from vomiting or diarrhea
  • Isolated potassium excess
Correct Answer Explanation
Toxic alcohols (methanol, ethylene glycol) and isopropyl alcohol are small molecules that contribute significantly to measured osmolality but are not accounted for in the standard calculated osmolality formula, producing an elevated osmolar gap — combined with an elevated anion gap metabolic acidosis (for methanol/ethylene glycol, via toxic acid metabolites), this pattern is an important clue to toxic alcohol ingestion.