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T4, FREE
MessageChemistry
Test Code
LAB127
Alias/See Also
Free T4
CPT Codes
84439
Preferred Specimen
Gold top (serum separator tube)
Minimum Volume
Whole blood: 700 uL (TWO full red-top microtainers).
Serum/plasma: 300 uL
Serum/plasma: 300 uL
Other Acceptable Specimens
Red Top tube acceptable
Specimen Stability
Refrigerated: 7 days
Frozen up to 4 weeks
Frozen up to 4 weeks
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Sodium heparin or Lithium heparin plasma and turbid sample: UNACCEPTABLE
Report Available
Same day
Limitations
Substances that bind to the thyroid hormone binding proteins are known to cause an increase in the
apparent free thyroid hormone concentration. In those cases, the change in FT4 concentration represents
the actual increases in free hormone and should not be considered an interference of the test.
Thyroid hormone autoantibodies in serum samples may cause interference in free-hormone
immunoassays. Results which are inconsistent with clinical observations indicate the need for additional
testing.
apparent free thyroid hormone concentration. In those cases, the change in FT4 concentration represents
the actual increases in free hormone and should not be considered an interference of the test.
Thyroid hormone autoantibodies in serum samples may cause interference in free-hormone
immunoassays. Results which are inconsistent with clinical observations indicate the need for additional
testing.
Reference Range
0.78 - 2.19 ng/dL
Performing Laboratory
Hoag Newport
