Desmopressin testing is used to differentiate central diabetes insipidus from nephrogenic diabetes insipidus. What is the expected response in central DI?

Desmopressin testing is used to differentiate central diabetes insipidus from nephrogenic diabetes insipidus. What is the expected response in central DI?

• A. Increased urine osmolality and decreased urine volume
• B. No change in urine osmolality
• C. Decreased urine osmolality
• D. Increased urine volume

Answer: (A)

The key idea is that central diabetes insipidus lacks ADH production, so giving an ADH analog will restore water reabsorption in the kidneys. Desmopressin acts on the collecting ducts to insert aquaporin-2 channels, increasing water reabsorption and concentrating the urine. In central DI, this leads to a higher urine osmolality and a smaller urine volume after the test. So the best outcome is increased urine osmolality with decreased urine volume following desmopressin. In contrast, nephrogenic DI would show little to no change because the kidney doesn't respond to ADH.

The key idea is that central diabetes insipidus lacks ADH production, so giving an ADH analog will restore water reabsorption in the kidneys. Desmopressin acts on the collecting ducts to insert aquaporin-2 channels, increasing water reabsorption and concentrating the urine. In central DI, this leads to a higher urine osmolality and a smaller urine volume after the test.

So the best outcome is increased urine osmolality with decreased urine volume following desmopressin. In contrast, nephrogenic DI would show little to no change because the kidney doesn't respond to ADH.