Pt has diabetes inspidus.
If urine concentrates with administration of ADH analog, the kidneys are responsive and the problem is with ADH production in the hypothalamus or release in the post. pituitary.
These always tripped me up:
+ Polydipsia= responds to water deprivation, low serum Na
+ Central= responds to vasopressin, high serum Na
+Nephrogenic = responds to nothing, normal serum Na