Thyroid Hormone Binding Ratio (THBR) / T3 Uptake
METHODOLOGY
Electrochemiluminescence Immunoassay (ECLIA)
PERFORMED
Tuesday & Friday
REPORTED
2 days
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 SPECIMENS
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.