Electrolyte Disorders USMLE Step 1 Practice Question
A 68-year-old man with a history of systolic heart failure (ejection fraction 32%) presents to the clinic with a 3-day history of progressive fatigue, mild confusion, and headache. He is currently on furosemide 40 mg daily, lisinopril, and spironolactone 25 mg daily. Vital signs are BP 128/78 mmHg, HR 92/min, RR 16/min, and temperature 37.1°C. On examination, he has normal skin turgor, no peripheral edema, and no orthostasis. Laboratory results are notable for: serum sodium 126 mEq/L, serum osmolality 265 mOsm/kg, urine osmolality 620 mOsm/kg, urine sodium 85 mEq/L, and fractional excretion of sodium 2.1%. Serum creatinine is 1.0 mg/dL (baseline 0.9 mg/dL). Which of the following is the most likely mechanism responsible for this patient's hyponatremia?
Answer choices
- AHypovolemic hyponatremia secondary to excessive loop diuretic use
- BHypervolemic hyponatremia from advanced renal failure and fluid retention
- CEuvolemic hyponatremia due to syndrome of inappropriate antidiuretic hormone secretionCorrect answer
- DPseudohyponatremia from severe hypertriglyceridemia
- EAcute nephrotic syndrome with secondary hyperaldosteronism and sodium retention
- FAcute kidney injury with oliguria and volume overload
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