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Test Code FT4 T4 (Thyroxine), Free

Important Note

Patients taking high doses of Biotin may have false elevated FT4 levels

Patients on heparin therapy may have false elevated FT4 levels

Performing Laboratory

Memorial Hospital Laboratory- Automated Procedures  304-388-5953       
Teays Valley Hospital Laboratory 304-757-1770
Plateau Medical Center Laboratory 304-469-8621

Specimen Requirements

Plasma-Mint Green, Dark Green Lithium Heparin or Serum-SST gold top, red top

Allow SST or red top to completely clot

Spin and physically separate plasma/serum from contact with cells as soon as possible

4 mL of plasma/serum (minimum 2 mL)

Specimen Rejection

  • Improperly labeled, collected, stored, and transported
  • Quantity not sufficient

Storage and Stability

Room temperature 15-30oC 8 hrs
Refrigerated 2-8oC 48 hrs
Frozen <-20oC Not specified

Reference Values

Age Range Reference Range (ng/dL)
0 days - <20 days 0.66-2.88
20 days - <3 yrs 0.74-1.38
3 yrs - <19 yrs 0.61-1.23
19 yrs - 150 yrs 0.6 - 1.3

Methodology

Chemiluminescent two-step immunoenzymatic assay

Days Test Set Up and Turnaround

Monday through Sunday, Continuously

AM Collection Expected by 9AM same day
Routine Expected within 24 hrs
Stat Expected within 1 hr
Timed Expected results are test dependant

CPT Coding

84439