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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 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

Analyte

Unit

Low

High

Age

N/A

N/A

N/A

N/A

N/A

CPT Codes

84436

LOINC Codes

3026-2

Volume

Preferred Volume: 0.5 mL

Minimum Volume: 0.2 mL

Specimen Stability

Storage Temperature

Stability

Room temperature

4 days

Refrigerated

8 days

Frozen

12 months

Collection Instructions

Collect specimen per standard laboratory collection procedures. 

 

Test Components

T4 Total (THYROXINE)

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.

Methodology

Electrochemiluminescence immunoassay (ECLIA)

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.

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

Synonyms/Keyword Search

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

Last Review Date

7/31/24