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?

1. A)Hypovolemic hyponatremia secondary to excessive loop diuretic use
2. B)Hypervolemic hyponatremia from advanced renal failure and fluid retention
3. C)Euvolemic hyponatremia due to syndrome of inappropriate antidiuretic hormone secretionGABARITO
4. D)Pseudohyponatremia from severe hypertriglyceridemia
5. E)Acute nephrotic syndrome with secondary hyperaldosteronism and sodium retention