This test is performed to confirm the diagnosis of Diabetes Insipidus in cases of polyuria, where blood and urine tests are unequivocal
It is not performed in newborns or young infants.
It is not performed if serum sodium is >150 meq/L
It should be performed only in hospital under medical supervision.
Period of water restriction
1-2 years 6-8 hours
>2 years 8-12 hours
Test is terminated when the end points are achieved
- Urine Sp Gravity >1.020 or urine osmolality >600 mOSm/Kg
- Plasma Osmolality >300 or serum sodium >150 mEq/L
- Loss of >4% body weight or signs of volume depletion
Children who continue to have impaired urinary concentration despite reaching the end points for plasma osmolality and serum sodium are given 120-250 mcg of desmopressin melt preparation sublingually or Inj Vasopressin 2.5-5U/Kg subcutaneously.
If urine osmolality increases to >800-Complete Central diabetes insipidus
If urine osmolality remains <600-Complete nephrogenic diabetes insipidus
If urine osmolality is between 600-800- it could be incomplete central or nephrogenic diabetes insipidus.
NORMAL OSMOLALITY RANGES
|Serum osmolality||285 to 295 mOsm/kg|
|Random urine osmolality||300-900m mOsm/kg|
|Urine, after 12-14 hrs water deprivation||> 850 mOsm/kg|