Endocrine dynamic function tests - water deprivation test
Three causes of polyuria
- Separates the three causes of hypotonic polyuria-polydipsia:
- AVP deficiency (AVP-D) - formerly cranial/central DI
- AVP resistance (AVP-R) - formerly nephrogenic DI
- Primary polydipsia
- Two parts, and both are needed:
1. Water deprivation - can the patient concentrate urine endogenously?
2. Desmopressin at the end - if not, is it the hormone or the kidney?
- *Superseded as the reference test by hypertonic saline-stimulated copeptin* where available - the water deprivation test misclassifies partial AVP-D and primary polydipsia in ~30% of cases
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