USC
ENDOCRINE LABORATORIES
TEST INDEX
TRIIODOTHYRONINE,
TOTAL (TT3)
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 80
– 180 ng/dL
CPT
Code 84480
Information:
Triiodothyronine
(T3) is the hormone principally
responsible for the effects thyroid hormone on the various target
organs. T3 (3, 5, 3’– triiodothyronine) is mainly
formed
extra-thyroidally, particularly in the liver, by enzymatic
5’–deiodination of T4. Accordingly, the T3
concentration in
serum is more a reflection of the functional state of the peripheral
tissue than the secretory performance of the thyroid gland. A reduction
in the conversion of T4 to T3 results in a fall in the Total T3
concentration. It occurs under the influence of medications such as
propanolol, glucocorticoids or amiodarone and in severe non-thyroidal
illness (NTI), and is referred to as the “low T3
syndrome”.
As with T4, over 99% of T3 is bound to transport proteins, primarily
TBG. However, the affinity of T3 to them is around 10-fold lower than
for T4. The determination of T3 is utilized in investigations
of
the etiology of hyperthyroidism.
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