This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Choose the best Lab value for a patient with central diabetes insipidus 
Select and explain. 
A. Urinary Osmolality - 50, Serum Osmolality - 300, B. Urinary Osmolality - 500, Serum Osmolality - 260, C. Urinary Osmolality - 50, Serum Osmolality - 260, D. Urinary Osmolality - 500, Serum Osmolality - 100
A: Urinary Osmolality - 50, Serum Osmolality - 300
Answer: A: Urinary Osmolality - 50, Serum Osmolality - 300 
Explanation: Diabetes insipidus is the reverse of SIADH, here the ADH level is decreased which leads to excessive water loss from the kidney resulting in hypertonic plasma associated with dilute urine.
It can be

- Central     → (due to impaired secretion of ADH from the neurohypophysis)
- Nephrogenic →   (due to renal insensitivity or nonresponsiveness to ADH).

In both circumstances. the serum osnzolality is increased with inappropriately low urine osmolalitv.
The two may be distinguished, however, by the response to either exogenous or endogenous vasopressin.
In neurogenic (central) DI,

- ADH levels are 100, and the kidney rapidly acts to conserve water once exogenous ADH is administered.

In contrast, in nephrogenic DI,

- ADH is associated with normal or increased ADHe levels and administration of additional ADH has no significant effect on renal water reabsorption.
Also known