T4 Free

Free T4; Thyroxine, Free

Mint Green Plasma Separator Tube

Tube Type

Test ID
LAB127
EPIC Order
T4, FREE
CPT Code(s)
84439
Group/Individual Test
Individual
Laboratory
Core Laboratory
Tube Station
30; STAT: 888
Specimen
Routine:
4 mL blood/Li Heparin plasma separator tube/Mint Green top. Also acceptable serum (Gold SST / Red Top Tube)
Micro:
0.9 mL blood/mint green top bullet/gold top/red top
Stability
Unspun: 8 hours
Spun/separated, Room Temperature-<8 hrs recommended
Spun/separated, Refrigerator: 48 hours
Spun/separated, Frozen: 30 days
Availability
Routine:
24 hrs/day
STAT:
Yes
Turnaround Time
Routine: 2 hrs; STAT: 1 hr
Reference Range
Normal:
T4 Free (ng/dL)
Age Range
<1 month Not Specified
1 month - 2 years 0.94-1.44
2 - 12 years 0.86-1.40
12 - 20 years 0.83-1.43
>20 years 0.89-1.76
Reference Ranges effective 7/13/2021
Comments
The anticonvulsant drug phenytoin may interfere with total and free T4 levels due to competition for TBG binding sites.
Results from patients taking biotin supplements should be interpreted with caution due to possible interference.
Thyroid autoantibodies in human serum may interfere and cause falsely elevated free T4 results.
Free T4 values may be decreased in patients with non-thyroidal conditions and in patients taking carbamazepine.

Reviewed by jcayless on December 28, 2021

Note: Reference ranges provided on this web site are for guidance only, and may not reflect the most recent changes. Refer to laboratory reports for current reference data.

UNC Hospitals
McLendon Clinical Laboratories
101 Manning Drive
Chapel Hill, NC 27514