Vasopressin test. This is a dehydration test for diabetes insipidus. First, fluid is withheld until urine osmolality is stable. Then 5 u of vasopressin is given by subcutaneous injection. The urine and plasma osmolality/concentration is measures before and one hour after the injection. Argenine vasopressin or avp given to these patients causes a >9% rise in urine osmolality. In normal patients, it is <9%.
During fluid deprivation test, the ADH (vasopressin) level dropped down to 1/3 of pre test level and below reference values. Is that a sign of diabetes insipidus?
Not necessarily. The most important thing to be following in a water deprivation test is the urine and serum osmolality. If the serum osmolality rises above normal, but the urine osmolality does not rise significantly, you have diabetes insipidus. Measuring ADH (vasopressin) levels can be unreliable.