Assessment of hormonal disorders of water metabolism

Clinical disorders of water regulation are relatively common and occur with severity ranging from profound and easily recognizable disturbance of body water balance to mild and often clinically inapparent. The development of sensitive and specific radioimmunoassay procedures capable of quantitating the level of AVP in plasma and urine has allowed elucidation of the pathophysiology of many of the disorders whether due to deficiency of ADH secretion and action or to excessive or persistent hormone release. In turn, the understanding of the factors regulating ADH release and action has led to establishment and validation of a variety of procedures that by indirect means allow estimation of extent of hormone action. These procedures based on physiologic influences that stimulate or inhibit ADH release or action are simple, readily available, and relatively inexpensive, and are capable of making an accurate diagnosis of a water-losing or water-retaining disorder. Properly performed and interpreted, such tests as water deprivation, saline infusion, comparison of urine and serum osmolality, and water loading can obviate the need for AVP immunoassays in evaluating most clinical disorders of water regulation. The immunoassay of AVP, although a valuable tool for the study of normal and pathologic physiology of ADH, is rarely necessary to firmly establish a clinical diagnosis and may itself be the source of misleading conclusions if its limitations are not fully appreciated.