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The University of Chicago Medicine Laboratories

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Mayo Clinic Laboratories

Test Code T4C T4 Total (Thyroxine) 

Important Note

This test may be affected by biotin interference. Patients on high dose biotin (5mg/day or more) should not have samples drawn until at least 24 hours after the last biotin administration

Specimen and Container/Tube

Specimen Type: Serum

Preferred Specimen: Red Top

Other Acceptable specimens: Serum/Gold Top, Plasma/Li-Heparin Mint Green Top, Plasma/Lavendar K2 Top, Plasma/Lavendar K3 Top

Specimen Stability

Storage Temperature

Stability

Room temperature

4 days

Refrigerated

8 days

Frozen

12 months

Collection Instructions

Collect specimen per standard laboratory collection procedures. 

 

Specimen Handling and Transport Instructions

UCMC Onsite Instructions: 

Collect specimen per standard collection procedure and send to laboratory immediately. 

 

UCMC Offsite and UC MedLab Outreach Instructions: 

  • Samples should be centrifuged within 2 hours of collection.
  • Centrifuge specimens at >2500 x g for 10 minutes at room temperature.
  • Aliquot sample into plastic transport tube containing a minimum of 0.2 mL of specimen.
  • Samples must be sent room temperature at 15-25oC.

Rejection Criteria

  • Common specimen rejected situations include: incorrect specimen type, insufficient volume, missing or incomplete specimen identifiers, incorrect specimen transport, or specimens outside stability limits. 
  • Specimens that are clotted or grossly hemolyzed.
  • Specimens that were transported unspun/whole blood and draw time is greater than 6 hours.

Reference Values

 

Test

Age

Sex

Reference Range*

T4

All

All

5.0-11.6 μg/dL

* Reference range is based on in-house studies performed at the University of Chicago Medicine by the Clinical Chemsitry Laboratories, per the Roche cobas 8000 modular analyzer series e 801 System Installation Workbook, and the e 801 T4 product insert.

Critical Values

Not applicable

Turnaround Time

Turnaround times are relative to the time the specimen is received in the test laboratory. 

 

STAT Turnaround Time: Not Available as STAT test

Routine Turnaround Time: 4 hours

Testing Schedule: 24/7

Clinical Indications

The determination of T4 can be utilized for the following indications: the detection of hyperthyroidism, the detection of primary and secondary hypothyroidism, and the monitoring of TSH-suppression therapy.

Test Components

T4 Total (Thyroxine) 

Methodology

Electrochemiluminescence immunoassay (ECLIA)

CPT Codes

84436

LOINC Codes

3026-2

Synonyms/Keyword Search

TT4, T4, T4, Total T4, Tetraiodothyronine, Thyroxine

Additional Information

  • Results should always be assessed in conjunction with patient's medical history, clinical examination and other findings.
  • The test cannot be used in patients receiving treatment with lipid-lowering agents containing D-T4. If the thyroid function is to be checked in such patients, the therapy should first be discontinued for 4-6 weeks to allow the physiological state to become re-established.
  • Autoantibodies to thyroid hormones can interfere with the assay.
  • Binding protein anomalies seen with FDH (familial dysalbuminemic hyperthyroxinemia), for example, may cause values which, while characteristic of the condition, deviate from the expected results.

Last Review Date

7/31/2024

Volume

Preferred Volume: 0.5 mL

Minimum Volume: 0.2 mL