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Test Name:
T4, Free

• SBMF No:
  30113
• Performance Lab Name:
  Automated Lab
• Test Mnemonic:
  FREE T4
• ABN:
  May be required – Medical Necessity
• CPT Code:
  84439
• LOINC Code:
  3024-7
• Also Known As:
  FT4
  Thyroxine, Free
  Free T4
• Spec Type:
  Serum
• Spec Container:
  Gold top (SST) or red top (serum) tube
• Alt Spec Type:
  Plasma
• Alt Spec Container:
  Green top (lithium heparin) tube
• Pref Vol:
  1.6 mL
• Min Vol:
  0.8 mL
• Fasting:
  No
• Spec Collect:
  Routine venipuncture
• Spec Process:
  Serum sample tubes, clot 30 minutes
  Promptly centrifuge 15 minutes
  Immediately transfer serum or plasma to separate plastic tube
  Properly centrifuged gel barrier tube sample does not require transfer of serum to separate tube
• Spec Store Transport:
  Refrigerated
• Spec Stability:
  1 week refrigerated (2-8°C)
  1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles
• Spec Remarks:
  Preferred specimen is primary serum sample contained in properly centrifuged gel barrier tube (not necessary to transfer serum to separate tube)
• Methodology:
  Electrochemiluminescent Immunoassay (ECLIA)
• Use:
  The determination of free thyroxine is an important element in clinical routine diagnostics
  Free T4 is measured together with TSH when thyroid function disorders are suspected
  The determination of FT4 is also suitable for monitoring thyrosupressive therapy
• Clinical Significance:
  

  The thyroid hormone thyroxine (T4) is physiologically part of the regulating system of the thyroid gland and has an effect on general metabolism. The major fraction of the total thyroxine is bound to transport proteins (TBG, prealbumin and albumin). The free thyroxine (FT4) is the physiologically active thyroxine component.The determination of free T4 has the advantage of being independent of changes in the concentrations and binding properties of the binding proteins; additional determination of a binding parameter (T-uptake, TBG) is therefore unnecessary.

  Also see:
  

• Reference Range:
  

  Free T4 ng/dL
  Age	Reference Range
  Less than 2 weeks	2.20-5.30 ng/dL
  2 weeks-20 months	0.90-2.20 ng/dL
  21-23 months	0.70-1.90 ng/dL
  2 years and older	0.80-1.80 ng/dL

• Day Run:
  Sun-Sat (daily)
• Time Run:
  As received
• Time Reported:
  4 hours
• Test Type:
  HORMONE