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Question 500
Endocrinology → General
Classification
Question
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A patient with diabetes insipidus is given antidiuretic hormone. The treatment is physiologically effective. Which change would be most consistent with a successful response?
Question Stem
Select the single best answer.
Options
A
A marked rise in urine flow with urine osmolality below plasma osmolality
B
No change in urine flow despite a rise in plasma osmolality
C
Approximately 80% reduction in urine flow with urine osmolality rising to about 600–900 mOsm/L
D
Increased urine flow with urine osmolality fixed at approximately 300 mOsm/L
E
Reduced urine flow accompanied by obligatory loss of free water
Explanation
Vasopressin increases water permeability in the distal tubule and collecting duct, increasing water reabsorption and reducing urine output. In a successful response to antidiuretic hormone in diabetes insipidus, urine flow may fall by approximately 80%, with urine osmolality rising to approximately 600–900 mOsm/L, around two to three times normal plasma osmolality.
Option Validity
A) Effective antidiuretic hormone reduces rather than increases urine flow and increases urine concentration.
B) A successful response should produce a substantial reduction in urine flow.
D) Effective treatment concentrates the urine above normal plasma osmolality rather than increasing urine flow.
E) Vasopressin promotes water conservation rather than obligatory free-water loss.
Further Reading
Saxena, MRCOG-1 Basic Sciences, Endocrinology: Hormones of the Posterior Pituitary - Vasopressin, pp. 306–307.