water-deprivation test

water-deprivation test
a test for diabetes insipidus in which fluid and food intake is withheld completely for (usually) 24 hours, with regular measurement of plasma and urinary osmolality and body weight. In a normal person the output of vasopressin will be increased in order to concentrate the urine as the plasma osmolality rises; correspondingly, the urine osmolality also rises and its volume diminishes. A patient with diabetes insipidus, however, will not achieve this: the urine osmolality will remain low and of high volume while the patient steadily dehydrates. The test must be abandoned if the patient loses 3% of body weight.

Medical dictionary. 2011.

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