Urine Osmolality

Urine Osmolality



Basic Information image



Definition


The solute concentration of a solution that may be expressed as moles of solute or osmoles of solute particles per kilogram of solvent, mol/kg and osmol/kg, respectively.



Typical Normal Range (US Units; SI Units)


600 to 1500 mOsm/kg, but is widely variable



Physiology


Sodium, chloride, and urea account for most of the osmotic activity in the urine. Large molecules (protein), cells, and casts contribute little to osmolality. The osmolality of urine is variable, and depends on the fluid and electrolyte balance of the body and the nitrogen content of the diet. In most urine samples, there is a linear relationship between urine specific gravity and osmolality.



Pearls




• The ratio of urine osmolality (Uosm) to plasma osmolality (Posm) is useful to determine the ability of the kidneys to concentrate or dilute urine.


• A Uosm:Posm ratio greater than 1 indicates that the kidneys are able to concentrate urine.


• A Uosm:Posm ratio of 1 indicates that water and solute are being excreted in a state that is iso-osmotic with plasma.


• A Uosm:Posm ratio significantly less than 1 indicates the kidneys are able to dilute urine.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Urine Osmolality

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