Electrolyte Disorders USMLE Step 1 Practice Question
A 32-year-old marathon runner collapses after finishing a race during which she drank large volumes of water but consumed no electrolyte containing fluids. She is confused and vomiting. Laboratory studies show sodium 122 mEq/L, serum osmolality 262 mOsm/kg, and urine osmolality 90 mOsm/kg. Which of the following is the most likely mechanism of her condition?
Answer choices
- AAldosterone deficiency causing renal sodium loss
- BOsmotic diuresis from uncontrolled diabetes mellitus
- CExcessive free water intake overwhelming renal excretionCorrect answer
- DExcess mineralocorticoid activity causing water retention
- ERenal tubular resistance to ADH
- FSyndrome of inappropriate ADH secretion causing water reabsorption in collecting ducts
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.