Suspect when polyuria and nocturia are not accompanied by diabetes mellitus.
High plasma osmolality and low urine osmolality. Plasma sodium is usually higher than normal.
In cases in which the osmolality levels and the sodium levels are equivocal then a water deprivation test should be conducted.
Again in cases where all the above are inconclusive a hypertonic saline infusion test.
Desamino-D-arginine vasopressin (DDAVP, desmopressin) is the treatment of choice.