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Test Code T4C T4-Thyroxine, Total, Serum

Important Note

Patients on high does biotin (>5mg/day) should not have samples drawn until at least 8 hours after the last biotin administration.

Specimen Type

Blood

Container/Tube

Red Top

Offsite Collection Instructions

  • Within 2 hours of collection the sample must be spun,
    aliquoted
    and transported refrigerated  (2 –
    8˚C).
  • Minimum volume of 250µl of serum

Turnaround Time

4 hours

Preferred Volume

4 mL

UCMC Collection Instructions

  • Unspun whole blood samples need to be received in the
    Laboratory Service Center within 2 hours of collection at room
    temperature  (15 – 25˚C).

STAT Turnaround Time

N/A

Test Usage

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.

Critical Results

N/A

Test Limitations

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.

Results should always be assessed in conjunction with
patient’s medical history, clinical examination and other
findings.

Whole blood/unspun specimens greater than 6 hours will
be
rejected. 

Additional Information

  • Gel Separator tubes need to be spun within 2 hours of
    collection and transported refrigerated (2 -
    8˚C).
  • Minimum volume of 250µL of plasma

 

Specimen
Container

Specimen Type

Container

Additive

Serum Preferred

Red Top

 None

Gold Top

 Gel separator

Plasma Acceptable

Mint Green

 Li Heparin Gel
separator

Dark Green

 Li Heparin

Specimen
Stability

Specimen Type

Storage
Temperature

Stability

Serum

Room Temperature  (15 -
25˚C)

N/A

Refrigerated  (2 -
8˚C)

7 Days

Frozen  (-20˚C)

1 Month

Plasma

Room Temperature  (15 -
25˚C)

N/A

Refrigerated  (2 -
8˚C)

7 Days

Frozen  (-20˚C)

1 Month

Fee Code

30184436

Synonyms

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

Specimen Minimum Volume

2 mL

DAY(S) AND TIME(S) PERFORMED

24 hours, 7 days a week including holidays.

STAT DAY(S) AND TIME(S) PERFORMED

N/A

CPT

84436

Method Name

Electrochemiluminescence immunoassay (ECLIA)

Reference Values

5.0 – 11.6 µg/dL