Diabetes Insipidus: When serum osmolality > 300 mOsm/kg and Urine osmolality < 300 mOsm/kg, in presence of significant polyuria and polydipsia. Often there may be hypernatremia, but older children might be able to maintain serum sodium in normal range by increasing their water intake.
Not Diabetes Insipidus: When serum osmolality <270 mOsm/kg and Urine osmolality >600 mOsm/kg.
Probably Diabetes Insipidus: When serum osmolality 270- 300 mOsm/kg and Urine osmolality 300-600 mOsm/kg, in presence of significant polyuria and polydipsia. In such cases, a water deprivation test needs to be performed under supervision of a Pediatric Nephrologist in a hospital setting.
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
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