Electrolyte Disorders USMLE Step 1 Practice Question
A 58-year-old man with schizophrenia is brought to the clinic because of fatigue and mild confusion. He reports drinking water almost continuously throughout the day. Laboratory studies show sodium 126 mEq/L, serum osmolality 265 mOsm/kg, and urine osmolality 65 mOsm/kg. Which of the following is the most likely explanation for this hyponatremia?
Answer choices
- ASIADH causing inappropriate water retention
- BOsmotic diuresis due to hyperglycemia
- CHypoaldosteronism causing renal sodium wasting
- DPrimary polydipsia causing dilution of serum sodiumCorrect answer
- ENephrogenic diabetes insipidus causing free water loss
- FThiazide diuretic use causing increased urinary sodium excretion
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