Days Set Up
Daily, 24 hours
Analytic Time

4 hours

MiChart Code
T4, Free
Soft Order Code

Test Updated:


Free T4 (Thyroxine)
Free Thyroxine
Synthroid (Levothyroxine)
Thyroxine, Free
Unbound T4

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Test Overview

Test Methodology

Chemiluminescent Immunoassay

Test Usage

Evaluation of thyroid function independent of binding protein status. Free T4 levels correlate with T4 secretion and metabolism. In hypothyroidism, FT4 is depressed and conversely, FT4 is raised in hyperthyroidism. Evaluating free T4 levels is useful when altered levels of total T4 occur due to changes in T4 binding proteins, especially TBG.

Reference Range

0.76 - 1.70 ng/dL

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Specimen Requirements

Collection Offsite

Collect specimen in a red top or SST tube. Centrifuge, aliquot serum into a plastic vial and refrigerate up to 48 hours or freeze for longer storage.

Yellow Top Tube
Normal Volume
0.5 mL serum
Minimum Volume
0.25 mL serum

Billing Information

CPT Code
Pro Fee Code

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Our High Standard

Quality that sets us apart

As the reference laboratory division of Michigan Medicine's Department of Pathology, MLabs shares the institution's commitment to applying established quality principles to clinical laboratory testing. Like other large organizations in complex, consequential fields, we rely on an established approach to monitor quality throughout the testing process.