This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
In a woman with polyuria of6L/day, which are the 2 most impoant investigations to be done - 
Select and explain. 
A. Water deprivation test, B. Water loading, C. Plasma and urine osmolality, D. Plasma osmolality
A: Water deprivation test
Answer: A: Water deprivation test 
Explanation: fluid deprivation test to differentiate which type of DI. If it is not significant administration of desmopressin required ( Harrison 17 pg 2219)