Hydration affects the result of a desmopressin test in adults.

Desmopressin tests to measure renal concentrating capacity, preceded by two different fluid regimens, have been compared in 19 adult subjects. The results show that peak osmolality in urine after 40 pg desmopressin intranasally is higher after fluid restriction. This observation confirms the need of a standardised fluid restriction before the desmopressin test.