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T4 Free
Test CodeAlias/See Also
Free T4 (Thyroxine)
Free Thyroxine
Thyroxine, Free
Preferred Specimen
Specimen Type: Serum
Collection Container: Serum gel
Specimen Volume: 3 mL
Minimum Volume
0.25 mL
Other Acceptable Specimens
Specimen Type: Plasma
Collection Container: Green top (Lithium heparin)
Instructions
Transport Container
Specimen Stability
Room temperature: Unacceptable
Refrigerated (on gel): 24 hours
Refrigerated (off gel): 6 days
Frozen: >6 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Samples stored on gel >24 hours, unlabeled, mislabeled, wrong tube type, QNS, severely hemolyzed samples, and any sample from which the lipid layer has not been removed.
Methodology
Chemiluminescent Microparticle Immunoassay (CMIA).
Setup Schedule
Daily
Report Available
Same day
Limitations
Free T4 assay is designed to have a mean potential interference from hemoglobin, bilirubin, triglycerides, and protein of < 10% at the levels indicated below:
Hemoglobin - ≤ 500 mg/dL
Bilirubin - ≤ 20 mg/dL
Triglycerides - ≤ 3000 mg/dL
Protein - ≤ 12 g/dL
NOTE: Performance of this test has not been established with neonatal specimens.
Reference Range
Clinical Significance
Performing Laboratory
Inova Laboratories
2832 Juniper Street
Fairfax, VA 22031
Last Updated: March 9, 2023
Last Review: N. Wolford, March 9, 2023