Excessive output of dilute urine from an antidiuretic hormone (ADH) abnormality is characteristic of __________.

Excessive output of dilute urine from an antidiuretic hormone (ADH) abnormality is characteristic of __________.

• A. Adrenal insufficiency
• B. Hyperthyroidism
• C. Diabetes insipidus
• D. Diabetes mellitus

Answer: (C)

Water balance is controlled by antidiuretic hormone. ADH makes the kidney’s collecting ducts reabsorb water; without enough ADH or if the kidneys don’t respond to it, water reabsorption drops and large volumes of urine that are very dilute are produced. This inability to concentrate urine is the hallmark of diabetes insipidus, leading to polydipsia and risk of dehydration. Diabetes mellitus causes polyuria through osmotic diuresis from high glucose, not from a failure of ADH to promote water reabsorption. Adrenal insufficiency and hyperthyroidism can affect fluid balance in other ways but do not produce the characteristic ADH-related dilute urine of diabetes insipidus.

Water balance is controlled by antidiuretic hormone. ADH makes the kidney’s collecting ducts reabsorb water; without enough ADH or if the kidneys don’t respond to it, water reabsorption drops and large volumes of urine that are very dilute are produced. This inability to concentrate urine is the hallmark of diabetes insipidus, leading to polydipsia and risk of dehydration. Diabetes mellitus causes polyuria through osmotic diuresis from high glucose, not from a failure of ADH to promote water reabsorption. Adrenal insufficiency and hyperthyroidism can affect fluid balance in other ways but do not produce the characteristic ADH-related dilute urine of diabetes insipidus.