T3 Uptake

Test Code

T3U

CPT Codes
84479

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) tube or Lithium Heparin Plasma (green top) tube

Transport Temperature

Room Temperature or Refrigeration

Specimen Stability

Room Temperature - 1 day; 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

Limitations

Metabolites of the drug Diclofenac may cause inappropriately elevated results in this test. Results from patients receiving this drug should be interpreted with caution. Thyroid hormone autoantibodies in samples may cause interference with this test. Results that are inconsistent with clinical observations indicate the need for additional testing.

Reference Range

23.0 - 40.5%

Clinical Significance

Thyroxine (T4) and triiodothyronine (T3) are transported in serum bound to protein, principally to thyroxine-binding globulin (TBG). The concentration of unoccupied thyroid hormone binding sites, for example, residual binding capacity, is inversely related to the total thyroid hormone concentrations. The main influence on metabolic control is exerted by the free thyroid hormone fraction. Free thyroid hormone concentrations can be measured directly, while an estimate can be made by using a binding capacity value, as measured by a T3 uptake or a T4 uptake test, to correct the total T3 or T4 concentration and obtain a free thyroid index (FT3I or FT4I). This is particularly important in conditions not associated with thyroid disease, where concentrations of the thyroid hormones or their binding proteins are altered, for example, in pregnancy.

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.