Water Deprivation Test

Question 1

How does the water deprivation test work?

Answer 1

Fluid restriction for 8 hours
Measure urine osmolality
Adminster desmopressin then measuring end osmolality

Question 2

What causes a high urine osmolality at the end of fluid restriction?

Answer 2

Normal because ADH will cause more water reabsorption, and mans the urin is more concentrated, resulting in a high urine osmolality.

Question 3

What causes a low urine osmolality at the end of fluid restriction?

Answer 3

Diabetes insipidus confirmed, either cranial or nephrogenic

Question 4

How to differentiate between types of diabetes insipidus?

Answer 4

Desmopressin test

Question 5

What causes a significant increase in urine osmolality after desmopressin?

Answer 5

Cranial diabetes insipidus

Question 6

What causes a non signficant increase in urine osmalitliy after desmopressin is given?

Answer 6

Nephrogenic because ADH levels is not the cause of the low urine osmolality

Question 7

What causes starting urine osmolality to be high before any fluid restriction?

Answer 7

Diabetes insipidus

Question 8

What causes starting urine osmolality to be low before any fluid restriction?

Answer 8

Primary polydipsia due to dilution