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water deprivation test
Indications:
- evaluation of diabetes insipidus (ADH deficiency)
Procedure:
- the bladder is emptied & baseline weight is recorded
- fluids are witheld
- serum sodium & plasma osmolality are measures every 2 hours
- urine volume, urine osmolality, & body weight are measured every hour
- the test is finished when
a) urine osmolality > 600 mOsm/kg
b) urine osmolility increase for 2 consecutive hours
c) plasma osmolality > 295 mOsm/kg
d) serum sodium > 145 meq/L
e) patient has lost > 5% of body weight
- if any of the test completion criteria are met before the test begins, the test is not recommended
- followed up with the desmopressin stimulation test when urine does NOT concentrate with water deprivation [1]
- the patient is then given desmopressin (see desmopressin stimulation test)
Interpretation:
- diagnosis of diabetes insipidus by
- a urine osmolality of < 600 mOsm/kg
- plasma osmolality > 295 mOsm/kg
- serum sodium > 145 meq/L
* also see desmopressin stimulation test
General
clinical procedure
References
- Medical Knowledge Self Assessment Program (MKSAP) 16, 17.
American College of Physicians, Philadelphia 2012, 2015