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Test Code TT4 / T4C T4 Total (THYROXINE)

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

Serum

Container/Tube

Red Top

Offsite Collection Instructions

1. Collect sample following standard collection methods
2. Within 2 hours of collection the sample must be spun and
aliquoted
3. Transport refrigerated  (2 – 8C).

Test Includes

N/A

Preferred Volume

0.5 mL

Specimen Minimum Volume

0.2 mL

Reject Due To

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

DAY(S) AND TIME(S) PERFORMED

24 hours, 7 days a week including holidays.

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.

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.

UCMC Collection Instructions

1. Collect sample following standard collection methods
2. Within 2 hours of collection the sample must be received in
Laboratory Service Center
3. Transport room temperature (15 – 25C).

Critical Results

N/A

Additional Information

N/A

Included in Additional codes

N/A

Coverage Information

N/A

Stability: Room Temp

n/a

Stability: Refrigerated

7 days

Stability: Frozen

1 month

Reference Values

5.0 – 11.6 µg/dL