USC
ENDOCRINE LABORATORIES
TEST INDEX
THYROID
HORMONE BINDING RATIO (THBR) / T3 UPTAKE
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 0.72
– 1.24 (no
units)
Interpretive
Data THBR (T3
Uptake)
increases with
increasing TBG.
CPT
Code 84479
Information:
The thyroid hormone thyroxine (T4) is the physiologically
active thyroid hormone that circulates bound to serum transport
proteins (TBG, prealbumin and albumin). Measurement of the total
thyroxine concentration only provides correct information on thyroid
status when the thyroxine-binding capacity in serum is normal. The free
thyroid hormones are in equilibrium with the hormones bound to the
carrier proteins. A change in the TBG concentration can lead to
elevated or lowered total T4 concentrations being measured although the
free T4 concentration is in the euthyroid range.
THBR tests provide an estimate of thyroid hormone binding proteins and
can be used to mathematically correct the total T4 concentration for
abnormal binding protein concentrations. Determinations of
the
free thyroxine Index (FT4I) from the quotient of total T4 and TBI
(thyroxine-binding index = result of the THBR determination) takes into
account changes in the thyroid hormone carrier proteins and the
thyroxine level.
THBR REQUESTS ARE ONLY USEFUL WHEN ORDERED TOGETHER WITH A TOTAL T4 OR
TOTAL T3 SO THAT THE FT4-INDEX OR FT3-INDEX CAN BE CALCULATED
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