Which DI type reacts to a water deprivation test?

• A. Central
• B. Nephrogenic
• C. Both
• D. Neither

Answer: (A)

During a water deprivation test, you’re evaluating how well the kidneys can concentrate urine and how the system responds to a dose of vasopressin (desmopressin) afterward. In central diabetes insipidus, there is a deficiency of ADH. Because the kidneys can respond to ADH, giving desmopressin after dehydration will cause a marked increase in urine concentration (urine osmolality rises) and a drop in volume. Nephrogenic diabetes insipidus, by contrast, features kidneys that don’t respond to ADH, so there’s little to no change after desmopressin. Therefore, the type that shows a response to the test is central diabetes insipidus.