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Test Code LAB127 Free T4 (Thyroxine)

Useful For

  •  Assessing thyroid status. Together with T3, it plays a vital role in regulating the body's metabolic rate, influences the cardiovascular system, growth and bone metabolism, and is important for normal development of gonadal functions and nervous system.  It should be measured together with TSH if thyroid disorders are suspected.
  • Monitoring thyrosuppressive therapy

Methodology

Electrochemiluminescence Immunoassay (ECLIA)

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Specimen Type: Plasma or serum
Container/Tube: Light-green top (lithium heparin gel), red top, or gold top
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL

Specimen Rejection: 

  1. Samples should not be taken from patients receiving therapy with high biotin doses (i.e. > 5 mg/day) until at least 8 hours following the last biotin administration.
  2. This test cannot be used in patients receiving treatment with lipid-lowering agents containing D‑T4.

Specimen Transport Temperature

Ambient/Refrigerated

Specimen Stability

Specimen Type Temperature Time
Plasma or Serum Ambient 5 days
  Refrigerated 7 days
  Frozen 30 days

Reference Values

1 month -23 months: 0.9-1.5 ng/dL

23 months - 12 years: 0.8-1.4 ng/dL

12 years - 20 years: 0.8- 1.3 ng/dL

20 years and older: 0.8-1.5 ng/dL

Additional Information

This test cannot be used in patients receiving treatment with lipid-lowering agents containing D‑T4. If the thyroid function is to be checked in such patients, the therapy should first be discontinued for 4‑6 weeks to allow the physiological state to become re-established.

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

84439