Water deprivation test used to differentiate the causes between diabetes insipidus and primary polydipsia.
Water deprivation test principle
The period after the administration of the desmopressin tests for the kidney’s ability to vasopressin and therefore differentiates between cranial and nephrogenic Diabetes Insipidus. The results of this test may be equivocal, necessitating further investigation.
Water deprivation test procedure
Following are the procedure steps.
- -Allow fluids overnight before the test and give a light breakfast with no fluid; no smoking permitted. Weigh the patien.
- Weigh the patien.
- Allow no fluid for 8h; patient must be under constant supervision during this time.
- Every 2 hours: Weigh the patient (stop the test if weight falls by >5% initial body weight)
- Patient empties the bladder. measure the volume and osmolality of the urine.
- Measure plasma osmolality stop the test if osmolality >30mmol/kg)
- After 8 hours, allow the patient to drink (no more than twice the urine volume during the period of fluid deprivation, to avoid acute hyponatraemia) and give 2µg desmopressin i.m.
- Measure the urine’s osmolality every 4 hours for a further 16 hours.