A deficiency in vasopressin can lead to which of the following?

• A. Euvolemic hypokalemia
• B. Euvolemic hyponatremia
• C. Diabetes insipidus
• D. Primary hypothyroidism

Answer: (C)

Vasopressin (antidiuretic hormone) controls water balance by promoting water reabsorption in the kidney’s collecting ducts. When vasopressin is deficient, the kidneys reabsorb less water, so a large volume of dilute urine is produced and plasma osmolality rises. This loss of free water with preserved or increased sodium leads to the clinical picture of diabetes insipidus.

The other options don’t fit because euvolemic hyponatremia arises from too much vasopressin causing water retention and dilutional low sodium, not a deficiency. Primary hypothyroidism is a separate endocrine problem and isn’t caused by vasopressin deficiency. Euvolemic hypokalemia is a potassium issue not directly tied to the action of vasopressin.