syndrome of inappropriate secretion of antidiuretic hormone

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syndrome of inappropriate secretion of antidiuretic hormone (SIADH) n. a condition of inappropriately high plasma levels of ADH (see vasopressin) with associated water retention, dilutional hyponatraemia, and the production of highly concentrated urine. Renal, adrenal, thyroid, and hepatic function are normal, as is the volume of circulating blood (euvolaemia). It is caused by a variety of pathological conditions and also by a number of drugs.