USC ENDOCRINE LABORATORIES

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TEST INDEX


Thyroglobulin (Tg) Tg Antibody TSH Free T4 Total T4 Free T3 Total T3 TPO Antibody
THBR FT4I or FT3I TBG Calcitonin PTH


FREE THYROXINE (FT4)

Methodology  Electrochemiluminescence Immunoassay

Performed  Mon - Fri

Reported  Same day

Collect  One 6mL RT (Min: 4mL RT)

Transport  1 mL refrigerated serum (Min: 0.5 mL)

Stability  Stored at 2 - 8°C until used; Stable if frozen at - 20°C

Unacceptable  Do not use heat-inactivated samples.

Reference Range  0.80 – 2.0 ng/dL

CPT Code  84439

Information: The thyroid hormone thyroxine (T4) is a physiologically active thyroid hormone and the principle secretory product of the thyroid gland, which 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) moiety is the physiologically active thyroxine component. The determination of FT4 is an important test in the clinical diagnosis and treatment of thyroid disorders.

The determination of free T4 has the advantage of being independent of changes in the concentrations and affinity of the thyroid hormone binding proteins (primarily TBG). The estimation of FT4 usually renders an additional binding protein ratio test (THBR) unnecessary.

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