Which test differentiates neurogenic DI from nephrogenic DI?

• A. Desmopressin Test
• B. AVP and Copeptin
• C. 3% hypertonic saline infusion and Copeptin
• D. Water deprivation test

Answer: (A)

The test relies on how the kidneys respond to a vasopressin analog. In central (neurogenic) DI, there isn’t enough endogenous AVP, so giving desmopressin replaces the missing hormone and the kidneys reabsorb more water. This leads to a noticeable rise in urine osmolality and a drop in urine volume. In nephrogenic DI, the kidneys don’t respond to AVP because of receptor or post-receptor defects, so desmopressin produces little to no change. A robust improvement after desmopressin therefore points to central DI, whereas little or no change points to nephrogenic DI. Desmopressin’s action is via the V2 receptors in the collecting ducts, promoting insertion of aquaporin-2 channels and increased water reabsorption.