Total T3, Total Triiodothyronine

Test Code

TT3

CPT Codes
84480

Preferred Specimen

Serum (gold top tube)

Minimum Volume

0.5 mL

Other Acceptable Specimens

Lithium Heparin Plasma (green top tube)

Transport Container

Serum (gold top) or Lithium Heparin Plasma (green top) Tube

Transport Temperature

Room Temperature or Refrigeration

Specimen Stability

Room Temperature - 24 hours; Refrigerated - 7 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Turbidity, Quantity Not Sufficient, IV contamination

Methodology
Chemiluminescence

Setup Schedule

Daily upon receipt

Report Available

Upon completion of analysis

Reference Range

0.97 - 1.69 ng/mL

Clinical Significance

Triiodothyronine is transported in serum primarily by thyroxine-binding globulin (TBG), approximately 99.5% of circulating T3 is protein-bound. T3 contributes significantly to the maintenance of the euthyroid state, 2 and the total T3 concentration has a role in screening for thyroid disease in conjunction with other tests. T3 alone cannot diagnose hypothyroidism, but it may be more sensitive than thyroxine (T4) for hyperthyroidism. A fall in T3 concentrations of up to 50% is known to occur in a variety of clinical situations, including acute and chronic disease. T3 concentrations may be altered in conditions affecting the capacity of the thyroid hormone binding proteins, e.g. pregnancy, when a test for T3 or T4 uptake may be used with the total T3 result to calculate the free T3 index (FT3I) to estimate the level of metabolically active free T3.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.