Physiology in Medicine: a Series of Articles Linking Medicine with Science

Diabetes insipidus is a condition in which patients produce large quantities of dilute urine. Central or neurogenic diabetes insipidus results from the failure of the posterior pituitary to make or secrete vasopressin (also called antidiuretic hormone [ADH]). Nephrogenic diabetes insipidus (NDI), which can be congenital or acquired, results from failure of the kidney to respond to vasopressin. Most adults with NDI have an acquired abnormality, with the most common causes being lithium therapy, hypercalcemia, hypokalemia, protein malnutrition, and release of ureteral obstruction. However, internists will be seeing more adult patients with congenital NDI because genetic screening of newborns in families with a history of this disorder has resulted in improved therapy for these children, and most are now surviving into adulthood. The standard method for diagnosing diabetes insipidus is a water deprivation test. Figure 1 shows the typical changes in urine osmolality in response to water deprivation and to the administration of exogenous vasopressin in healthy individuals and in patients with diabetes insipidus. This test, which also distinguishes between persons with complete versus partial versions of each type of diabetes