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Test Code SQ FT4C, EPIC LAB127 T4 (Thyroxine), Free, Plasma

Important Note


Patients receiving therapy with high biotin doses (i.e. > 5 mg/day), could cause a +/- 10% change in their test results. It is recommended by Roche that samples should not be drawn until at least 8 hours following the last biotin administration.


This test cannot be used for patients receiving treatment with lipid-lowering agents containing D-T4.

Performing Laboratory

Meriter Laboratories

Specimen Requirements

Specimen Type:

Preferred: Plasma

Acceptable: Serum

Container/Tube: Light-green top (lithium heparin gel)

Specimen Volume: 1 mL

Collection Instructions:

1. If patient is taking thyroid medications, draw specimen at least 10 hours after dose.


Specimen Transport Temperature

Refrigerated/Frozen OK

Reference Values

<3 days: 0.8-3.4 ng/dL
3-30 days: 0.8-3.0 ng/dL
1-11 months: 0.8-2.6 ng/dL

1-5 years: 0.8-2.2 ng/dL
6-10 years: 0.8-2.0 ng/dL

≥11 years: 0.8-1.8 ng/dL

Day(s) Test Set Up

Monday through Sunday

Analytical Time


1 hour


4 hours

Test Classification and CPT Coding


Specimen Requirements Additional Information



Specimen Stability:Sample is stable refrigerated (2° C-8° C) for 7 days, and frozen (≤-20° C) for 30 days. Freeze only once.


Stability of serum obtained with tubes containing separating gel: 48 hours at 2° C-8° C.

Reporting Title

Free T4