A desmopressin challenge that increases urine osmolality most strongly supports which disorder?

A desmopressin challenge that increases urine osmolality most strongly supports which disorder?

• A. Nephrogenic DI
• B. SIADH
• C. Primary polydipsia
• D. Central DI

Answer: (D)

Desmopressin (DDAVP) challenges test how well the kidney can concentrate urine when vasopressin signaling is present. In central diabetes insipidus, there is a lack of endogenous vasopressin, but the kidneys retain the ability to respond to it. When DDAVP is given, the collecting ducts respond by inserting aquaporin-2 channels, increasing water reabsorption and markedly raising urine osmolality. In contrast, nephrogenic DI involves kidneys that don’t respond to vasopressin, so DDAVP produces only a minimal rise in osmolality. Primary polydipsia features suppressed ADH due to excess water intake, so the response to DDAVP is less dramatic. SIADH already has high ADH with concentrated urine, so additional DDAVP doesn’t substantially change osmolality. Therefore, a large increase in urine osmolality after the desmopressin challenge most strongly supports central DI.

Desmopressin (DDAVP) challenges test how well the kidney can concentrate urine when vasopressin signaling is present. In central diabetes insipidus, there is a lack of endogenous vasopressin, but the kidneys retain the ability to respond to it. When DDAVP is given, the collecting ducts respond by inserting aquaporin-2 channels, increasing water reabsorption and markedly raising urine osmolality. In contrast, nephrogenic DI involves kidneys that don’t respond to vasopressin, so DDAVP produces only a minimal rise in osmolality. Primary polydipsia features suppressed ADH due to excess water intake, so the response to DDAVP is less dramatic. SIADH already has high ADH with concentrated urine, so additional DDAVP doesn’t substantially change osmolality. Therefore, a large increase in urine osmolality after the desmopressin challenge most strongly supports central DI.