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ID:144 Osmolality (urine)
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DescriptionA measure of urine tonicity / concentration
IndicationInvestigation of polyuria.
Additional InfoPrimary polydipsia can cause a low urine osmolality and should be considered as a cause particularly in psychiatric patients. Primary polydipsia will be associated with a dilutional hyponatraemia. With primary polydipsia urine may remain dilute even with fluid restriction but serum osmolality is often low or low to normal. A prolonged water deprivation test may be required.
Concurrent Testsna
Dietary Requirementsna

InterpretationA urine osmo >750 mOsmol/Kg excludes DI as a cause of polyuria (in classic DI serum osmolality increases >300 and urine osmolality remains <350 mOsmol/Kg). However, a low urine osmolality is NOT diagnostic of DI.

Ref. Range (Male)
Ref. Range (Female)
Ref. Range (Paed)
Ref. Range Notes
UnitsmOsmol/Kg


IP Acute TATRefer to Website
IP Routine TATRefer to Website
GP Acute TAT- Contact Laboratory
GP Routine TATRefer to Website
Turnround CommentOsmolality analysis will only be treated as urgent if the lab is contacted, and in such instances will have a TAT of 3hrs
Originally edited by : JHB. Last edited on 10/04/2019 14:13:20. Published By S.Bennett on 10/04/2018 14:13:20.