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Test Code T4FRER T4, Free LAB127

Performing Laboratory

UnityPoint The Finley Hospital

Performance

Testing is performed Monday through Sunday.

Routine: Typically completed within 4 hours after the specimen arrives at the laboratory.

STAT: Typically completed within 2 hours after the specimen arrives at the laboratory.

Specimen Requirement

  1. Lithium heparin plasma (Green) is the specimen of choice. 500μL.
  2. Serum (Red/Gold) and EDTA (purple) plasma are also acceptable sample types.
  3. Gel tubes are acceptable.
  4.  It is recommended that the serum or plasma be separated from contact with cells within 2 hours from time of collection.
  5. Free T4 specimens are stable for 5 days at 20-25°C, 7 days at 2-8°C, and 30 days at -20°C.

Useful For

Thyroxine (T4) is the main thyroid hormone secreted into the bloodstream by the thyroid gland. Together with triiodothyronine (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.

T4 circulates in the bloodstream as an equilibrium mixture of free and serum bound hormone. Free T4 (fT4) is the unbound and biologically active form, which represents only 0.03 % of the total T4. Free T4 is a useful tool in clinical routine

diagnostics for the assessment of the thyroid status. It should be measured together with TSH if thyroid disorders are suspected and is also suitable for monitoring thyrosuppressive therapy.

Reference Values

Reference range established for patients > 18 yrs:
0.92 -1.68 ng/dL

Method

Chemiluminescent immunoassay (Competitive binding principle); Roche cobas Pro

CPT Information

84439: Chemistry: Thyroid Tests Thyroxine; Total free

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