A 22-year-old man presents to the clinic due to excessive urination. He goes to the restroom almost every 15 minutes. His physical examination is otherwise normal. Laboratory tests show
Serum Na: 140 mEq/L
Urine output: 4 L/24 hours
Urine is negative for glucose and protein and no pus cells
Urine Na: 18 mEq/L
Urine osmolality: 260 mOsm/kg after 4h fluid deprivation.
What is the most likely diagnosis?
D-Urinary tract infection
Urine deprivation test shows urine osmolality lower than 400 mOsm/kg, which is diagnostic for diabetes insipidus. It is >800 in normal person and >500 in polydipsia. Absence of glucose and pus in urine excludes DM and UTI respectively.
The correct answer is B