After dDAVP, collect urine for osmolality hourly for 4 h.

After dDAVP, collect urine for osmolality hourly for 4 h.


Normal Response

Urinary osmolality rises and urine volume decreases with water deprivation. The U:P should be 2.0 or greater at completion of the test. The rise in plasma osmolality does not exceed 295 mosM/kg.

Cranial Diabetes Insipidus

The urinary osmolality fails to rise appropriately and urine volumes do not show the normal decrease. U:P is less than 2.0. In general the plasma osmolality exceeds 295 mosM/kg. The urinary osmolality rises swiftly after exogenous dDAVP administration.

Primary Polydipsia

The urinary osmolality rises and a U:P >2.0 is achieved, provided there is adequate dehydration. A prolonged WDT is necessary if sufficient dehydration is not achieved.

Nephrogenic Diabetes Insipidus

The urinary osmolalities fail to rise and the urine volumes fail to decrease. The plasma osmolality may rise to greater than 295 mosM/kg. dDAVP administration does not result in a rise in urinary osmolality.

Note: In cases of mild diabetes insipidus, a prolonged WDT may be necessary.

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