Which test helps determine the etiology of hypernatremia?

Which test helps determine the etiology of hypernatremia?

• A. Water deprivation
• B. ACTH stimulation test
• C. Oral glucose tolerance test
• D. Dexamethasone suppression test

Answer: (A)

Determining the cause of hypernatremia hinges on the kidney’s ability to concentrate urine when free water is scarce. The water deprivation test directly tests this by withholding water and tracking changes in urine osmolality and volume as plasma osmolality rises. If urine remains dilute despite dehydration, diabetes insipidus is likely, indicating a defect in the body’s ability to conserve water; if urine concentrates appropriately, the hypernatremia is more likely due to insufficient water intake or excessive water loss elsewhere. If DI is suggested, desmopressin can then differentiate central from nephrogenic DI, guiding etiology and management. The other options assess adrenal function, cortisol excess, or glucose tolerance, which do not address the kidney’s concentrating ability or the primary cause of hypernatremia.

Determining the cause of hypernatremia hinges on the kidney’s ability to concentrate urine when free water is scarce. The water deprivation test directly tests this by withholding water and tracking changes in urine osmolality and volume as plasma osmolality rises. If urine remains dilute despite dehydration, diabetes insipidus is likely, indicating a defect in the body’s ability to conserve water; if urine concentrates appropriately, the hypernatremia is more likely due to insufficient water intake or excessive water loss elsewhere. If DI is suggested, desmopressin can then differentiate central from nephrogenic DI, guiding etiology and management. The other options assess adrenal function, cortisol excess, or glucose tolerance, which do not address the kidney’s concentrating ability or the primary cause of hypernatremia.