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


TRIIODOTHYRONINE, TOTAL (TT3)

Methodology  Electrochemiluminescence Immunoassay

Performed  Mon - Fri

Reported  Mon - Fri

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  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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