The syndrome of inappropriate antidiuretic hormone is characterized by the following

(A) Hyponatremia and urine sodium excretion > 20 meq/l # Syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH) is defined by the hyponatremia and hypo-osmolality resulting from inappropriate, continued secretion or action of the hormone despite normal or increased plasma volume, which results in impaired water excretion.# Diagnosis:> In the absence of a single laboratory test to confirm the diagnosis, SIADH is best defined by the classic Bartter-Schwartz criteria, which can be summarized as follows: Hyponatremia with corresponding hypo-osmolality Continued renal excretion of sodium Urine less than maximally dilute Absence of clinical evidence of volume depletion Absence of other causes of hyponatremia Correction of hyponatremia by fluid restriction> Cardinal features of SIADH include: Hyponatremia (dilutional hyponatremia with Na+ <135 mmol/l) Decreased plasma osmolality (<280 m osm/kg) with inappropriately increased urine osmolality > 150 m osm). Urine sodium over 20 meq/l Low Blood urea Nitrogen < Wmg/L Hypouricemia (<4mg/dL) 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.