Skip Ribbon Commands
Skip to main content
Sign In

26517 Free Thyroxine (500454)

Free Thyroxine (500454)
Test Code: ZFT-4
Synonyms/Keywords

​​​​​​​Thyroxine, Free T4, Free T-4, Tetraiodothyronine

Test Components

Thyroxine (T-4), Serum

Thyroxine, Free (fT4)

Useful For

​*THIS TEST IS AVAILABLE FOR PEDIATRIC PATIENTS

If Thyroxine, Free (Free T-4) testing is requested for an adult please order in-house test code T4-FREE. 

Specimen Requirements
Fasting RequiredSpecimen TypePreferred Container/TubeAcceptable Container/TubeSpecimen VolumeSpecimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)

​Serum
​Serum Separator Tube (SST)
​Red Top Tube (RTT)
​1 mL
​0.4 mL
Collection Processing Instructions

​Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Serum must be separated from cells within 45 minutes of venipuncture.  Send serum in a plastic transfer tube.  FREEZE.

Specimen Stability Information
Specimen TypeTemperatureTime

​​​Serum




​Frozen (preferred)
​200 days

​Refrigerated
​7 days


​Ambient
Rejection Criteria

​Plasma or whole blood samples received.

Interference

​This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Performing Laboratory Information
Performing LocationDay(s) Test PerformedAnalytical TimeMethodology/Instrumentation

​LabCorp of America
​Monday through Friday
​1 day
Immunoassay/ Siemens Centaur
Test Information

​Testing is performed at Esoterix Endocrinology Lab (a division of LabCorp).  

Reference Range Information

 Thyroxine (T-4)
                             ​
Age:  Range
Premature(26 - 30w) Day 3 - 4:  2.6 - 14.0
Full-term Day 1 - 3:  8.2 - 19.9
1 week:  6.0 - 15.9
1 - 11m:  6.1 - 14.9
12m -  2y:  6.8 - 13.5
3 -  10y:  5.5 - 12.8
11 - 17y:  4.9 - 13.0
Adults:  4.2 - 13.0


Thyroxine, Free (fT4)
                                
Age:  Range
<4d:  0.66 - 2.71
4d - 1m:  0.83-3.09
1 - 11m:  0.48 - 2.37
1 - 5y:  0.85 - 1.75
6 - 10 y:  0.90 - 1.67
11 - 19y:  ​0.93 - 1.60
>=20y:  0.82 - 1.77
Outreach CPTs
CPTModifier
(if needed)
QuantityDescriptionComments

​84436




​Thyroxine, total


84439​






​Thyroxine, free
Synonyms/Keywords

​​​​​​​Thyroxine, Free T4, Free T-4, Tetraiodothyronine

Test Components

Thyroxine (T-4), Serum

Thyroxine, Free (fT4)

Ordering Applications
Ordering ApplicationDescription

​Cerner
​​Free T-4 (500314)​

If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Fasting RequiredSpecimen TypePreferred Container/TubeAcceptable Container/TubeSpecimen VolumeSpecimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)

​Serum
​Serum Separator Tube (SST)
​Red Top Tube (RTT)
​1 mL
​0.4 mL
Collection Processing

​Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Serum must be separated from cells within 45 minutes of venipuncture.  Send serum in a plastic transfer tube.  FREEZE.

Specimen Stability Information
Specimen TypeTemperatureTime

​​​Serum




​Frozen (preferred)
​200 days

​Refrigerated
​7 days


​Ambient
Rejection Criteria

​Plasma or whole blood samples received.

Interference

​This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Useful For

​*THIS TEST IS AVAILABLE FOR PEDIATRIC PATIENTS

If Thyroxine, Free (Free T-4) testing is requested for an adult please order in-house test code T4-FREE. 

Test Components

Thyroxine (T-4), Serum

Thyroxine, Free (fT4)

Reference Range Information

 Thyroxine (T-4)
                             ​
Age:  Range
Premature(26 - 30w) Day 3 - 4:  2.6 - 14.0
Full-term Day 1 - 3:  8.2 - 19.9
1 week:  6.0 - 15.9
1 - 11m:  6.1 - 14.9
12m -  2y:  6.8 - 13.5
3 -  10y:  5.5 - 12.8
11 - 17y:  4.9 - 13.0
Adults:  4.2 - 13.0


Thyroxine, Free (fT4)
                                
Age:  Range
<4d:  0.66 - 2.71
4d - 1m:  0.83-3.09
1 - 11m:  0.48 - 2.37
1 - 5y:  0.85 - 1.75
6 - 10 y:  0.90 - 1.67
11 - 19y:  ​0.93 - 1.60
>=20y:  0.82 - 1.77
For more information visit:
Performing Laboratory Information
Performing LocationDay(s) Test PerformedAnalytical TimeMethodology/Instrumentation

​LabCorp of America
​Monday through Friday
​1 day
Immunoassay/ Siemens Centaur
For billing questions, see Contacts
Outreach CPTs
CPTModifier
(if needed)
QuantityDescriptionComments

​84436




​Thyroxine, total


84439​






​Thyroxine, free
For most current information refer to the Marshfield Laboratory online reference manual.