AVP and Hyponatremia: Laboratory tests showed that the patient had severe hyponatremia (sodium {Na}: 121 mmol/L), low serum osmolality (252 mOsm/kg), inappropriately elevated urine osmolality (748 mOsm/kg), elevated urinary sodium (112 mEq/L), hypouricemia (1.9 mg/dL), and a fractional excretion of uric acid of 11.66%, consistent with syndrome of inappropriate antidiuretic hormone secretion.