hormonal and metabolic disorders
ArginineVasopressin Deficiency (Central Diabetes Insipidus)
Diagnosis ofArginineVasopressinDeficiency
Water deprivation test deficiency in people who produce large amounts of urine. They first test the urine for sugar to rule out Diabetes Mellitus (DM) (a more common cause of excessive urination). Blood tests show abnormal levels of many electrolytes, including a high level of sodium. Thewater deprivation testis the best test to diagnoseargininevasopressindeficiency. In a water deprivation test, urine production, blood electrolyte levels, and weight are measured regularly for a period of about 12 hours, during which the person is not allowed to drink. A doctor monitors the person's condition throughout the course of the test. At the end of the 12 hours—or sooner if the person has a decrease in blood pressure, an increase in heart rate, or a loss of more than 5% of body weight—the doctor stops the test and injectsvasopressin. The diagnosis ofargininevasopressindeficiency is confirmed if, in response tovasopressin, the person's excessive urination stops, the urine becomes more concentrated, the blood pressure rises, and the heart beats more normally. The diagnosis of nephrogenic diabetes insipidus is made if, after the injection, the excessive urination continues, the urine remains dilute, and blood pressure and heart rate do not change. Doctors sometimes measure the level of circulatingvasopressinor copeptin (a piece of thevasopressinhormone) in the blood to confirmargininevasopressindeficiency. However,vasopressinand copeptin levels are difficult to measure, and the tests are not routinely available. Copeptin andvasopressinlevels determined without water deprivation are generally not helpful in diagnosis. Additionally, the water deprivation is so accurate that direct measurement ofvasopressinor copeptin is usually unnecessary. 