Triiodothyronine, Total (TT3)
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
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.