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Epic Test Code LAB127 T4, Free: Serum

Performing Location(s)

BMC

Synonyms

Free Thyroxine, Unbound T4

Specimen Type

Serum

Preferred Container

Gold or Red top tube

Blood Tube Draw Volume

Min 50% draw volume  

Minimum Volume to Submit for Testing

1 mL Serum

  • Multiple test can be performed from this volume. For question please contact the lab at 547-3975.  

Storage Requirements

Sample tubes should be centrifuged within 2 hour of collection followed by transfer of the serum (red or gold top) or plasma (green top) to a labeled plastic, aliquot tube.

See Causes of Rejection for temperature requirements.

Transportation Needs

 Deliver specimen to laboratory within 1 hour of collection if unspun. If not possible see "storage Requirements". 

Causes for Rejection

Mislabeled or unlabeled specimen
Less than 50% draw for Vacutainer tubes
> 48 hours Refrigerated
> 8 hours Room Temperature
> 6 months Frozen
Hemolysis > 1000 mg/dL HgB
Lipemia > 1800 mg/dL Trig
Bilirubin > 10 mg/dL Bili
EDTA,NaF,Oxalate
High levels of Biotin
>400 mg/dL Cholesterol

Reference Values

Population Units Reference Range
All populations ng/dL 0.6-1.3

 

Additional Information

Additional Information: Reflexive Thyroid Testing Protocol

Thyroid function tests are ordered whenever there is suspected thyroid disease or for the management of patients on replacement therapy. The introduction of sensitive thyrotropin (sTSH) in the early 1990’s has transformed thyroid function testing from thyroxine-based strategies to sTSH strategies. The American Thyroid Association (ATA) and the National Academy of Clinical Biochemists (NACB) have recommended that serum sTSH level be the first test, complemented by an appropriate free thyroxine (FT4) estimate. This strategy represents the best and most efficient combination of blood tests for diagnosis and follow-up of most patients with thyroid disorders.

 

Accordingly, the Bassett Healthcare Clinical Laboratories will be providing reflexive thyroid function testing using the following algorithm

 

 

T3 is recommended for patients with suppressed sTSH and normal FT4. T3 is not recommended in patients with normal or increased sTSH

Most thyroid testing is performed on out-patients. The ATA does not recommend thyroid screening in sick hospitalized patients, unless clinically significant thyroid disease is suspected.

This algorithm has been approved by Endocrinology.

 

 

Reflex Testing Information

 

 

                                                                         

 

Limitations

Specimens must be free of particulate matter. To prevent the appearance of fibrin in serum samples, complete clot formation should take place before centrifugation. If clotting time is increased due to thrombolytic or anticoagulant therapy, the use of plasma specimens will allow for faster sample processing and reduce the risk of particulate matter.

 

Interference from icterus (biliruin 10 mg/dL), hemolysis (hemoglobin 1000 mg/dL (monomer)) and lipemia (triglyceride 1800 mg/dL was less than 10%.

 

The following substances cross-react with the FT4 method at the concentrations indicated:

 

Substance

Concentration (ug/dL)

% Cross Reactivity
L-T4 5 >100%
D-T4 10 71%

L-Triiodothyronine

600

0.00%

R- Triiodothyronine

100

0.10%

Tetraiodothyroacetic Acid

25

4%

 

Available STAT

Yes

Days of Analysis

All

Methodology

Beckman AU/Dx Series

CPT Code

84439

Last Updated

25-Apr-22 BHD