Unit Code 9257:
Osmolality, Body Fluid
Useful For
To help determine the source and type of fluid
Clinical Information
Osmolality is an index of the solute concentration. It is determined
by the number and not by the nature of the particles in solution.
Dissolved solutes change the physical properties of solutions;
they increase the osmotic pressure and decrease freezing point.
Body fluids have the same osmolality as a corresponding serum
sample taken at the same time. "True body fluids" include: ascitic,
cerebrospinal, hydrocele, edema, pericardial, pleural, spermatocele
and synovial fluids. Secretions not in equilibrium with the extra-
cellular fluids of the body include gastric juice, saliva and sweat.
Serum osmolality is normally between 275-295 mosmol/kg; it
increases with dehydration and decreases with overhydration.
Urine osmolality reflects the ability of the kidney to maintain tonicity
and water balance. The normal kidney can concentrate a urine to
800-1,400 mosmol/kg, and with excess fluid intake, a minimal
osmolality of 40-80 mosmol/kg can be obtained.
Reference Values
No established normal values
Interpretation
No normals are available.
Cautions
Avoid viscous fluids
Clinical Reference
Clinic Diagnosis and Management by Laboratory Methods. 20th
edition. Edited by JB Henry. Philadelphia, WB Saunders
Company, 2001
External
link
PDF
document
Excel
document
Word
document