Osmolality, Body Fluid

CPT CODE:

USEFUL FOR:

To help determine the source and type of fluid

SPECIMEN REQUIRED:

1   mL of body fluid. Send specimen refrigerated.Note:  Indicate specimen source on request form.

TRANSPORT TEMPERATURE:

Frozen\Refrig OK\Ambient NO

CLINICAL INFORMATION:

Osmolality is an index of the solute concentration. It is determinedby 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 serumsample taken at the same time. "True body fluids” include: ascitic,cerebrospinal, hydrocele, edema, pericardial, pleural, spermatoceleand 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; itincreases with dehydration and decreases with overhydration.Urine osmolality reflects the ability of the kidney to maintain tonicityand water balance. The normal kidney can concentrate a urine to800-1,400 mosmol/kg, and with excess fluid intake, a minimal osmolality of 40-80 mosmol/kg can be obtained.

CLINICAL INTERPRETATION:

No normals are available.

REFERENCE VALUES:

No established normal values