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Endocrine
·
hard
Water Deprivation Test
Flowchart
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Distinguish primary polydipsia, central DI, nephrogenic DI.
Decision
Outcome
Decision
Water deprivation test setup?
✓
No water 2–3 h prior; measure urine volume/osm hourly, serum Na/osm q2h
Decision
Urine osmolality after deprivation?
✓
>600 mOsm/kg → primary polydipsia
✓
Stable on 2–3 hourly measurements with plasma osm >295 or Na >145 → administer desmopressin
Outcome
Primary polydipsia — behavioral, fluid restriction
Decision
Urine osmolality response to desmopressin?
✓
↑ 50–100% → central DI
✓
Small or no increase → nephrogenic DI
Outcome
Central DI — desmopressin; MRI for sellar lesion
Outcome
Nephrogenic DI — stop lithium if responsible; low-Na diet, thiazide, amiloride