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Osmolality, Blood

Plasma Osmolality, Serum Osmolality, Osmolality, Serum/Plasma

Test Codes

EPIC: LAB5096, Beaker: OSMO, Antrim: 17109

Department

Chemistry

Specimen Collection Criteria

FOR EC AND INPATIENT SAMPLE COLLECTION ONLY:

Preferred Sample:  One Light Green (Mint)-top Plasma Separator Tube (PST) (Minimum Whole Blood: 4.0 mL)

Acceptable Sample:  One Gold-top SST (Minimum Whole Blood: 4.0 mL)

FOR PHYSICIAN OFFICE/OUTREACH SAMPLE COLLECTION:

COLLECT:  One Gold-top SST (Minimum Whole Blood: 4.0 mL) 

Contact Laboratory for acceptability of other tube types.
See Minimum Pediatric Specimen Requirements for Microtainer^® collection.

Physician Office/Draw Specimen Preparation

• Let SST specimens clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection. (Minimum: 0.2 mL)
• Centrifuge Green-top tube immediately to separate plasma from cells. Transfer 2.0 mL plasma to a plastic transport tube and refrigerate (2-8°C or 36-46°F) within two hours of collection. (Minimum: 0.2 mL)

Preparation for Courier Transport

Transport: Centrifuged SST tube or 2.0 mL plasma, refrigerated (2-8°C or 36-46°F). (Minimum: 0.2 mL)

Rejection Criteria

• Red-top tubes with serum not separated from cells within two hours of collection.
• Green-top tubes with plasma not separated from cells within two hours of collection.

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST tubes, Green-top tubes, or Microtainers^® to separate serum or plasma from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes Green-top Tubes, and Microtainers^® without Separator Gel
Room Temperature (20-25°C or 68-77°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Plasma Specimens (Aliquots)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days 

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Dearborn Chemistry Laboratory

Farmington Hills Chemistry Laboratory
Grosse Pointe Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory
Troy Chemistry Laboratory

Performed

Sunday – Saturday, 24 hours a day.
STAT results available within 1 hour of receipt in the Laboratory.
Routine results available within 24 hours.

Reference Range

275-295 mOsmol/kg.

Test Methodology

Freezing Point Depression.

Interpretation

• An increased serum osmolality may occur with hypernatremia, dehydration, hyperglycemia, azotemia and volatile ingestion.
• Low serum osmolality may be due to overhydration, hyponatremia and syndrome of inappropriate ADH secretion.

Clinical Utility

Serum osmolality is used to evaluate acutely ill or comatose patients. An increased osmolal gap (difference between measured and calculated osmolalities of greater than 10) may indicate ingestion of ethanol, ethylene glycol, methanol, isopropanol or other toxin. Serum osmolality is also used to evaluate electrolyte and water balance, hyperosmolar status, dehydration and seizures.

CPT Codes

83930

Contacts

Last Updated

10/29/2023