Free Thyroxine

Test Code

FT4

Alias/See Also

Free T4

CPT Codes
84439

Preferred Specimen

SST

Minimum Volume

0.5 mL

Transport Container

Serum (gold or red top) Tube

Transport Temperature

Room Temperature or Refrigeration

Specimen Stability

Room Temperature - 1 Day; Refrigeration - 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

0.78 - 2.19 ng/dL

Clinical Significance

The free fraction of the circulating thyroxine (T4) is considered to exert the main influence on metabolic control. Consequently, the FT4 concentration is believed to be the most direct indicator of an individual’s thyroid status. FT4 concentrations are generally depressed in hypothyroidism and raised in hyperthyroidism. Measurement of FT4 thus provides an aid to the differential diagnosis of thyroid disease. FT4 concentrations are independent of the concentration of thyroid hormone binding proteins and may therefore be measured in patients with elevated or reduced binding protein concentrations without the need for additional tests of binding capacity. In borderline cases of suspected thyroid malfunction, additional tests such as free T3 or TSH may be necessary.

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.