A 6-year-old boy presents with polyuria and polydipsia. Serum sodium is 152 mEq/L, urine osmolality is 90 mOsm/kg. After desmopressin administration, urine osmolality rises above 600 mOsm/kg. This response confirms which diagnosis?

• A Nephrogenic diabetes insipidus
• B Primary polydipsia
• C Central diabetes insipidus ✓
• D Syndrome of inappropriate ADH secretion

Explanation

Desmopressin is a V2 receptor agonist that increases aquaporin-2 insertion in the collecting duct. A rise in urine osmolality greater than 50 percent after desmopressin indicates functioning renal V2 receptors and absent endogenous ADH, confirming central diabetes insipidus. In nephrogenic diabetes insipidus the receptors or aquaporins are defective and there is no significant response, while SIADH presents with concentrated urine rather than polyuria.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.