Diagnosis of DI can be made by an overnight water deprivation test. This test requires the patient to eliminate fluid intake for a fixed period of time, usually around 8–12 hours. If the first morning void is not highly concentrated, the patient is diagnosed with DI. Central DI usually can be treated with a synthetic replacement of ADH, called desmopressin. Desmopressin is taken to control thirst and frequent urination. Although there is no substitute for nephrogenic DI, it may be treated with careful regulation of fluid intake.