Water deprivation test
Last updated: Wednesday, 31, March, 2004
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| Item | Process |
|---|---|
| Specimen | Urine; 2 mL blood in a lithium heparin tube collected at intervals during the test. |
| Protocol | Medical supervision must be provided during the test, which must be performed in a hospital setting. The patient is allowed no oral or parenteral intake. Plasma and urine specimens are collected hourly until osmolality reaches a plateau (<30 mmol/kg increase over 1 hour) or the patient becomes dehydrated (body weight decrease >3%). Desmopressin is then given and a further urine specimen is taken. |
| Reference Interval | Urine osmolality >2 x plasma osmolality with <9% increase after DDAVP. |
| Application | Diagnosis of central or nephrogenic diabetes insipidus. |
| Interpretation | Complete central diabetes insipidus: urine osmolality remains lower than plasma osmolality with >50% increase after DDAVP. Partial central diabetes insipidus: urine shows 10-50% increase in osmolality after DDAVP. Nephrogenic diabetes insipidus: urine osmolality <2 x plasma osmolality with <9% increase after DDAVP. Psychogenic polydipsia may resemble nephrogenic diabetes insipidus, but the patient is usually hypo-osmolar and hyponatraemic. |
| Reference | Miller M et al. Ann Int Med 1970; 73: 721-729. C Heetham T and Baylis PH. Paediatr Drugs 2002; 4(12): 785-796. |