The syndrome of inappropriate antidiuretic hormone is characterized by the following :

Answer is A (Hyponatremia and urine sodium excretion > 20 meq/l) : Cardinal features of SIADH include: Hyponatremia (dilutional hyponatremia with Na+ < 135 mmol/1) Decreased plasma osmolality (150 m osm). Urine sodium over 20 meq/1 Low Blood urea Nitrogen < 10 mg/L Hypouricemia ( Clinical Euvolemia - Absence of sign of hypervolemia (edema, ascitis) - Absence of signs of hypovolemia (ohostatic hypotension, tachycardia, features of dehydration) Absence of cardiac, liver or renal disease Normal thyroid and adrenal function A high BUN suggests a volume contracted state and excludes a diagnosis of SIADH. Q