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HelpTest Code LAB107 Osmolality, Blood
Performing Laboratory
St. Louis Children's Hospital - Chemistry
Specimen Requirements
Patient Preparation: None
Container/Tube
Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube
Acceptable: Full Green samplette/microtainer, plain red-top tube, or Gold SST gel tube
Collection Volume: 2.0 mL (minimum 0.6 mL)
Submission Container/Tube: If specimen is coming from outside facility and collected in a microtainer or plain red-top tube aliquot processed sample into a plastic vial for transport (labeling with specimen type).
Special Instructions: Keep at ambient temperature and send to lab promptly.
Sample Rejection
Specimens that are hemolyzed
Mislabeled or unlabeled specimens
Logistics
Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 2 hours from receipt in performing lab
Reference Values
Therapeutic Range: 275-300 mOsm/kg
Critical Values: ≤ 260 mOsm/kg OR ≥ 330 mOsm/kg
Critical test results will be automatically called back initially and every 24 hours thereafter.
Methodology
Freezing Point Depression
Limitations
- Hemoglobin and other intracellular components will falsely elevate the osmolality.
Additional Information
FOR SLCH CORE LABORATORY USE ONLY
Lab Processing Instructions: Centrifuge specimen to separate ASAP. If specimen is collected in a plain, red-top or microtainer aliquot sample into a plastic tube for testing (labeling with specimen type).
Processed Volume: 0.3 mL plasma/serum
Analyte Stability:
| Specimen Type | Temperature | Time | |
|---|---|---|---|
| Whole Blood (unprocessed) | Ambient | 4 hours | |
| Plasma/Serum (processed) | Refrigerated (preferred) | 5 days | |
| Ambient | 4 hours | ||
| Frozen | 6 months |
NOTE: keep sample at ambient temperature prior to testing
Test Classification and CPT Coding
83930
LOINC
2692-2
Last Reviewed
06/2025