THYROXINE, FREE

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Note: This test is sensitive to Biotin and result may be falsely elevated in patients taking high doeses.

Test Code

T4F

Alias/See Also

FT4; Free Thyroxine; Thyroid; Free T4

CPT Codes
84439

Preferred Specimen

1 Gold tube (gel separator)

Minimum Volume

0.2 mL

Other Acceptable Specimens

or 1 Green tube (Lithium Heparin)

Instructions

Centrifuge for complete separation of serum or plasma and red cells within 2 hours.

Transport Temperature

Refrigerate

Specimen Stability

2-8°C up to 7 days
15-30°C up to 8 hours
Frozen samples are stable - do not freeze whole blood

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

Quantity not sufficient

Methodology

Chemiluminescent immunoassay

Setup Schedule

M, T, W, Th, F, Sa, Sun

Report Available

Within 24 hours of receipt at the performing laboratory.

Reference Range

Age	ng/dL
0-3 days	0.70 - 2.70
4 - 29 days	0.80 - 3.10
1-23 months	0.60 - 2.12
2 - 6 years	0.60 - 1.60
7 - 11 years	0.60 - 1.50
12 - 17 years	0.60 - 1.40
Adult	0.55 - 1.60

Clinical Significance

FT4 aids in the diagnosis of hyper/hypothyroidism. In conjunction with TSH can determine if the feedback loop is intact. Includes only FT4 and is unaffected by protein levels.

Performed By
Alverno Laboratories

Performing Laboratory
Alverno Central Lab
NCHB2 (Chemistry, Beckman DxI)

Last Updated: June 7, 2023

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.