Syndrome of inappropriate antidiuretic hormone secretion

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is characterized by excessive release of antidiuretic hormone from the posterior pituitary gland or another source. The increase in blood volume (hypervolemia) often results in dilutional hyponatremia in which the plasma sodium levels are lowered and total body fluid is increased. Although the sodium level is low, SIADH is brought about by an excess of water rather than a deficit of sodium.