USC
ENDOCRINE LABORATORIES
TEST INDEX
FREE
THYROXINE (FT4)
Methodology
Electrochemiluminescence Immunoassay
Performed
Tue, Fri
Reported
Same day
Collect
One 6mL
RT (Min: 4mL RT)
Transport
2 mL refrigerated serum
(Min: 0.8 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
– 2.00 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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