Antidiuretic hormone (ADH), also called arginine vasopressin (AVP), is a hormone that helps regulate water balance in the body by controlling the amount of water the kidneys reabsorb while they are filtering wastes out of the blood. Increased ADH is seen in hypovolemia, hypertension, severe physical stress, SIADH (syndrome of inappropriate ADH secretion), Central nervous system tumours or infection and pneumonia Decreased levels of ADH are noted in diabetes insipidus and psychogenic water intoxication.