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Water deprivation test interpretation — SCE Endocrinology MCQ

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ModerateEndocrine emergencies/dynamic testsWater deprivation test interpretationSCE Endocrinology

A 31-year-old man has polyuria. Water deprivation raises urine osmolality from 90 to 105 mOsm/kg; desmopressin raises it to 650 mOsm/kg. Serum sodium is 150 mmol/L. What is the most likely diagnosis?

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Correct answer: B — Cranial diabetes insipidus

Failure to concentrate during deprivation with strong desmopressin response indicates cranial DI. Nephrogenic DI would show minimal response to desmopressin. Hypernatraemia supports water loss rather than primary polydipsia.

Reference: Society for Endocrinology Diabetes Insipidus Guidance