This MedLibrary.org supplementary page on Plasma osmolality is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (August 2008) |
Plasma osmolality is a measure of the concentration of substances such as sodium, chloride, potassium, urea, glucose, and other ions in human blood. It is calculated as the osmoles of solute per kilogram of solvent. Normal reference range of osmolality in plasma is about 280 - 303 milli-osmoles per kilogram. It is affected by changes in water content.
To calculate plasma osmolarity (osmolality) use the following equation:
Posm = 2[Na+ + [Glucose]/18 + [ BUN ]/2.8
The above equation holds true if the glucose & ureas blood chemistry units are given as: mg/dL.
If the units are given as: mmol/l; then the calculated osmolality is given by:
P.OSM = 2[NA] + 2[K+] + [Urea] + [Glucose]
Osmolality can be measured on an analytical instrument called an Osmometer. It works on the method of depression of freezing point.
The Osmolar gap is the diffence between the measured osmolality and the calculated osmolality.
Clinical Relevance
As cell membranes in general are freely permeable to water, the osmolality of the extracellular fluid (ECF) is approximately equal to that of the intracellular fluid (ICF). Therefore, plasma osmolality is a guide to intracellular osmolality. This is important, as it shows that changes in ECF osmolality have a great affect on ICF osmolality - changes that can cause problems with normal cell functioning and volume. If the ECF was to become too hypotonic, water would readily fill surrounding cells, increasing their volume and potentially lysing them (cytolysis).
 |
This medical article is a stub. You can help Wikipedia by expanding it. |
|
||||||||||||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 25 October 2008, at 08:46.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Plasma osmolality".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.