AVP and Central diabetes insipidus: Diabetes insipidus is defined as the passage of large volumes (> 3 L/24 h or 2 L/m2/24 h) of dilute urine with reduced urine osmolality (< 300 mOsm/kg) and is caused by reduced or absent secretion of pituitary antidiuretic hormone arginine vasopressin or by a poor kidney response to the hormone.