Which test is used to differentiate central from nephrogenic diabetes insipidus?

Which test is used to differentiate central from nephrogenic diabetes insipidus?

• A. Desmopressin challenge
• B. Water deprivation
• C. Serum cortisol
• D. ACTH stimulation

Answer: (A)

Differentiating central from nephrogenic diabetes insipidus relies on assessing the kidney’s response to ADH replacement. In central DI there is an ADH deficiency, so giving desmopressin, a synthetic vasopressin analogue, should markedly raise urine osmolality and reduce urine volume as the kidneys reabsorb more water. In nephrogenic DI the kidneys are unresponsive to ADH due to receptor or signaling defects, so there is little or no change in urine osmolality or volume after desmopressin. The water deprivation test helps confirm DI by showing an inability to concentrate urine, but it doesn’t distinguish the cause as specifically as the desmopressin challenge. Serum cortisol and ACTH stimulation test adrenal function and are not used to differentiate DI types.

Differentiating central from nephrogenic diabetes insipidus relies on assessing the kidney’s response to ADH replacement. In central DI there is an ADH deficiency, so giving desmopressin, a synthetic vasopressin analogue, should markedly raise urine osmolality and reduce urine volume as the kidneys reabsorb more water. In nephrogenic DI the kidneys are unresponsive to ADH due to receptor or signaling defects, so there is little or no change in urine osmolality or volume after desmopressin. The water deprivation test helps confirm DI by showing an inability to concentrate urine, but it doesn’t distinguish the cause as specifically as the desmopressin challenge. Serum cortisol and ACTH stimulation test adrenal function and are not used to differentiate DI types.