What best differentiates central diabetes insipidus from nephrogenic diabetes insipidus?

• A. Central DI is due to kidney insensitivity to ADH
• B. Central DI responds to desmopressin with decreased urine output only in nephrogenic DI
• C. Central DI causes hyponatremia; nephrogenic causes hypernatremia
• D. Central DI is due to low ADH; nephrogenic DI is due to kidney insensitivity to ADH

Answer: (D)

Central diabetes insipidus and nephrogenic diabetes insipidus are differentiated by whether ADH is missing or the kidneys fail to respond to it. In central DI, the posterior pituitary doesn’t secrete enough ADH, so circulating ADH is low and the kidneys can’t concentrate urine. In nephrogenic DI, ADH is present (often normal or high), but the kidneys are insensitive to it due to receptor or aquaporin defects, so urine remains dilute despite ADH. The statement that best captures this difference is that central DI is due to low ADH, whereas nephrogenic DI is due to kidney insensitivity to ADH. A desmopressin challenge helps confirm: central DI typically shows a substantial rise in urine osmolality and a drop in urine volume after desmopressin, while nephrogenic DI shows little to no improvement.