Nephrogenic diabetes insipidus is characterized by which of the following?

Nephrogenic diabetes insipidus is characterized by which of the following?

• A. Inability of the kidney to respond normally to vasopressin
• B. Increased responsiveness to vasopressin
• C. Decreased serum osmolality
• D. Elevated urine-specific gravity

Answer: (A)

Nephrogenic diabetes insipidus occurs when the kidney cannot respond to vasopressin (antidiuretic hormone). Vasopressin normally acts on the collecting ducts to insert aquaporin-2 channels, increasing water reabsorption and concentrating urine. In nephrogenic DI, the renal response to vasopressin is blunted, so free water reabsorption fails, leading to large volumes of dilute urine, rising serum osmolality, and polydipsia. That’s why the best description is the inability of the kidney to respond normally to vasopressin. If the kidney were more responsive to vasopressin, urine would be more concentrated rather than dilute. A decreased serum osmolality would reflect excess free water, not DI, and elevated urine-specific gravity indicates concentrated urine, which DI does not have.

Nephrogenic diabetes insipidus occurs when the kidney cannot respond to vasopressin (antidiuretic hormone). Vasopressin normally acts on the collecting ducts to insert aquaporin-2 channels, increasing water reabsorption and concentrating urine. In nephrogenic DI, the renal response to vasopressin is blunted, so free water reabsorption fails, leading to large volumes of dilute urine, rising serum osmolality, and polydipsia. That’s why the best description is the inability of the kidney to respond normally to vasopressin.

If the kidney were more responsive to vasopressin, urine would be more concentrated rather than dilute. A decreased serum osmolality would reflect excess free water, not DI, and elevated urine-specific gravity indicates concentrated urine, which DI does not have.