The Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH)

Summary 

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a disorder of water balance characterized by hypotonic hyponatremia and impaired water excretion. The diagnosis of SIADH is based on the exclusion of other hyponatremic conditions, the presence of hyposmolality with inappropriate urine osmolality and a urine sodium concentration usually above 30 mEq/L. Some simple and readily available biologic parameters can be helpful in the diagnosis of SIADH (low urea and uric acid levels). The recent syndrome of nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is also discussed and the association of asymptomatic hyponatremia with falls and bone fractures.

Keywords: Hyponatremia, uric acid, urea, bicarbonate, ADH, fall