UOSMB - Clinical: Osmolality, Body Fluid

Test Catalog

Test Name

Test ID: UOSMB    
Osmolality, Body Fluid

Useful For Suggests clinical disorders or settings where the test may be helpful

Determining the source and type of fluid

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Osmolality is a measure of dissolved solute particles in solution and is determined by the number, and not by the nature, of the particles in solution. Dissolved solutes change the physical properties of solutions, increasing the osmotic pressure and boiling point, and decreasing the vapor pressure and freezing point.


Body fluids have the same osmolality as a corresponding serum sample taken at the same time.(1) "True body fluids" include: ascitic, cerebrospinal, hydrocele, edema, pericardial, pleural, spermatocele and synovial fluids. Secretions not in equilibrium with the extracellular fluids of the body include gastric juice, saliva, and sweat.(1)

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

No established reference values

Interpretation Provides information to assist in interpretation of the test results

Not applicable

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Cannot be performed on viscous fluids.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Clinical Chemistry: Principles and Techniques. Edited by R Henry, D cannon, J Winkelman.Harper and Row, NY. 1974, p 738-739

2. Todd-Sanford Clinical Diagnosis by Laboratory Method., 17th edition. Edited by I Davidsohn, JB Henry. 1984, pp 122-123; 393-395

3. Osmometry and Cryoscopy School Outline. Advanced Instruments. Newton Highlands, Massachusetts 02161

4. Torres-Pinedo R, Lavastida M, Rivera CL, et al: Studies on Infant Diarrhea, J Clin Invest 1966;45:469-480

5. The Advance Osmometer Model 3250 User’s guide