[Skip to Content]

Osmolality, Blood (OSMS)

Send to a FriendPrint Page

EPIC Test Name

OSMOLALITY,BLOOD

EPIC Code

LAB107

Specimen Requirements

plasma
Minimum Volume:0.5 mL
Collection:Collect using standard laboratory procedures
Transport:Room Temperature ASAP
Stability:Room Temperature: 48 hours at 20-25 degrees C
Refrigerated: 48 hours at 2-8 degrees C
Container:LIT GRN
Processing/Storage:Centrifuge, pour off, and refrigerate plasma.
Rejection Causes:Hemolysis,
Insufficient Sample Volume, lipemic samples

Methods

Freezing point depression

Turnaround Time

SpecimenTurnaround TimeFrequency
plasmaRoutine: 4 hours24/7

Reference Ranges

Freezing point depression
All RangeUnitCritical Values
285-295 mOsm/kgmOsm/kg<250 and >340 mOsm/kg

Clinical Indications

• Osmolality is a physical property of a solution. The concentration of solutes or solute particles, e.g., Na, Glucose, urea, glucose, etc. in a patient sample contributes to the osmotic pressure of the sample. Osmotic pressure governs the movement of solvent, e.g., water, across cellular membranes that are permeable to water molecule, but not large protein molecules.
• Osmolality increases with dehydration and decreases with overhydration. The intravenous fluids given to a patient should have a physiological osmolality.
• Osmolal gap (OG) is the difference between the osmolality measured in the chemistry laboratory and the osmolarity calculated from the major molecules in the patient sample, e.g., sodium, chloride, glucose and urea. An osmolal gap is often used in assessing if a patient ingested or is exposed to an exogenous osmotic substance, e.g., methanol, isopropanol, ethylene glycol.

OG = measured osmolality – calculated osmolarity
Where Calculated osmolarity = 2 [Na+] + 2 [K+] + Glucose + Urea (BUN), all in mmol/L
or
Calculated osmolarity = 2 [Na+] + Glucose + Urea (BUN), all in mmol/L

Common Synonyms

Osmolality, Serum OSMS

Performed

Lab
Chemistry - Downtown

Interpretative Information

Generally, an osmolal gap > 10 indicaes the presence of unaccounted low-molecular-weight osmotically active substances, e.g., ethylene glycol in the serum sample of an ethylene glycol intoxicated patient.

Measured osmolality is normally in range of 275-295 mOsm/kg
A normal ratio of serum sodium to serum osmolality is between 0.43 and 0.5. This may be abnormally distorted in drug intoxication.

CPT

83930

LOINC

2692-2

References

1. Schindler, EI, Brown, SM and Scott, MS: Electrolytes and Blood Gases. In Rifai N, Horvath AR and Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 8th ed. St. Louis, MO: Elsevier, 2019.
2. https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/614057

Contact Information

Chemistry - Downtown: (315)464-4460
Top