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Water Deprivation Test
- free fluid overnight
- start at 8am
- light breakfast
- no caffeine / no smoking
- no fluids for 8 hours (dry food only)
- hourly measurements
- plasma osmolality
- urine volume
- urine osmolality
- body weight (STOP test if >3% body weight lost)
- after 8 hours give 2 microgrammes of desmopressin
Normal
- urine concentrates to >800mOsm/kg
- little response to desmopressin
In diagnosis of
- Diabetes Insipidus
- distinguishes cranial (response to desmopressin) or nephrogenic cause
- Psychogenic Polydipsia
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