Electrolyte Disorders USMLE Step 1 Practice Question
A 34-year-old man presents to the emergency department with altered mental status and tachypnea. He reports ingesting a large quantity of aspirin 2 hours ago in a suicide attempt. Vital signs are: BP 118/76 mmHg, HR 108/min, RR 24/min, temperature 38.2°C, SpO2 98% on room air. Laboratory studies show: arterial pH 7.25, PCO2 28 mmHg, HCO3- 12 mEq/L, serum glucose 98 mg/dL, serum sodium 138 mEq/L, serum potassium 4.2 mEq/L. Calculated serum osmolality based on standard formula is 295 mOsm/kg, but direct measurement of serum osmolality is 325 mOsm/kg. Which of the following unmeasured solutes is responsible for the elevated osmolar gap in this patient?
Answer choices
- AAcetone from accelerated ketogenesis
- BEthylene glycol metabolites
- CSalicylate ions from aspirinCorrect answer
- DEthanol from concurrent ingestion
- EMethanol or formic acid metabolites
- FIsoniazid-induced metabolic byproducts
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.