Water Deprivation Test in Hypopituitarism	

The rise in plasma osmolality resulting from lack of fluid for a period of several hours stimulates ADH secretion; this forms the basis of the standard eight-hour water deprivation test that is used in the diagnosis of diabetes insipidus (Fig. 2.23). The test should be performed during the day when careful observation is possible, since severe fluid and electrolyte depletion can occur. Urine and plasma osmolality are measured for eight hours, after which time a synthetic analogue of ADH, desmopressin, is given intramuscularly. The urine osmolality is then remeasured. 

See also:
• Investigation of Polyuria