Central DI Water Deprivation Test Interpretation — ESENeph MCQ

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EasyElectrolyte DisordersCentral DI Water Deprivation Test InterpretationESENeph

A 45-year-old woman presents with polyuria (6 L/day), polydipsia, and serum sodium 152 mmol/L. A water deprivation test shows urine osmolality rising from 150 to 620 mOsm/kg after desmopressin administration. What is the diagnosis?

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Correct answer: C — Central (cranial) diabetes insipidus

In a water deprivation test, the urine fails to concentrate during water deprivation (urine osmolality remains low at 150 mOsm/kg), indicating diabetes insipidus. After desmopressin (synthetic ADH), urine osmolality rises significantly to 620 mOsm/kg (>50% increase), confirming that the kidneys CAN respond to ADH — the problem is inadequate ADH production. This is central (cranial) diabetes insipidus. In nephrogenic DI, desmopressin would produce <10-50% rise in urine osmolality. In primary polydipsia, the urine would concentrate during water deprivation alone (before desmopressin). MRI of the pituitary is indicated to assess for structural causes.

Reference: Fenske & Allolio 2012 – Diabetes Insipidus Diagnosis; JRCPTB 2022 – Nephrology Curriculum