ADH, also called vasopressin, is a hormone synthesized in the hypothalamus.

It is stored in the pituitary gland.

Release is regulated by central nervous system (CNS) and chest baroreceptors, which detect changes in blood volume and pressure.

ADH acts on the kidneys to increase total body water.

Secretion normally occurs in the presence of hypovolemia.

ADH secretion in euvolemic patients results in syndrome of inappropriate secretion of antidiuretic hormone (SIADH), with increased excretion of sodium, resulting in hyponatremia, and retention of water.

Pulmonary diseases, especially pneumonia

CNS illnesses—stroke, hemorrhage, traumatic injury, infection

Paraneoplastic production of ADH by a tumor

Certain chemotherapy agents

Exogenous administration of vasopressin or desmopressin

Psychiatric medications

Symptoms generally occur only when hyponatremia is severe, that is, ≤ 120 to 125 mEq per L.

Early symptoms include malaise, anorexia; gastrointestinal symptoms such as nausea, vomiting, diarrhea; muscle cramps.

Late symptoms are due to CNS effects of hyponatremia—headache, blurred vision, irritability, lethargy, confusion, deteriorating mental status, decreased reflexes, seizure, coma.

Death may also occur.

Low plasma sodium, that is, hyponatremia

High urine sodium (” class=LK href=”javascript:void(0)” target=right xpath=”/CT{06b9ee1beed59419a81e5e1e1a4f60b0cc8cd1057525de73425b2b43f4df7f1b507a1084f7ea9b0f017d2cd1c12460ee}/ID(AB1-M10)”>>40 mEq/L)

Low plasma osmolality (<A onclick="get_content(event,'AB1-M12'); return false;" onmouseover="window.status=this.title; return true;" onmouseout="window.status=''; return true;" title="<280 mOsm/kg)