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Osmolality Serum

Order Code CH253
Turnaround Time 24-48 hours
Test Includes

Osmolality Serum

Specimen Requirements
Specimen Source
Transport Container
(Specimen Container)

SST (Tiger Top)

Preferred Specimens
Collection Instructions
(Transport Temperature)
Transport at Room Temperature
Specimen Stability
Temperature Period
Room temperature 7 days
Refrigerated 7 days
Frozen 28 days
Reject Criteria

Gross hemolysis
Heparinized plasma

Test Details
Spectrophotometry, Ion-Selective Electrode (ISE), calculation
Clinical Significance

Osmolality is a measure of the number of dissolved solute particles in solution.It 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.The osmolality of serum increases with dehydration and decreases with overhydration. The patient receiving intravenous fluids should have a normal osmolality. If the osmolality rises, the fluids contain relatively more electrolytes than water. If the osmolality falls, relatively more water than electrolytes is being administered.Normally, the ratio of serum sodium, in mEq/L, to serum osmolality, in mOsm/kg, is between 0.43 and 0.5. The ratio may be distorted in drug toxication.Generally, the same conditions that decrease or increase the serum sodium concentration affect the osmolality.A comparison of measured and calculated serum osmolality produces a delta-osmolality. If this is >40 mOsm/kg a H2O in a critically ill patient, the prognosis is poor.

Reference Ranges

280 – 301 mOsmol/kg