Thyroxine, Free

Alternative Names/Synonyms	Free T4, FT4, T4
Laboratory	Core Laboratory & Transfusion Medicine
Sub-section	Biochemistry
Specimen Type	Blood
Test Code	FT4S2, FT4P2

Clinical Significance (If applicable)

Assisting in the diagnosis of primary and secondary thyroid function disorders, non-thyroidal illness and TSH resistance syndrome.

Monitoring response to therapy in hyperthyroid or thyroid cancer patients.

Specimen Requirements (Sample Type)

Serum, Plasma

Specimen Requirements (Volume (mL))

0.5 mL

Specimen Requirements (Tube Type)

Serum (Gold SST)
Plasma (Light Green PST)
Collection Containers – Tube Types

Draw (mL)

4.5 mL

Collection Requirements

Test cannot be used in patients treated with lipid-lowering agents containing D-Thyroxine.
Collection Instructions

Sample Stability

Room Temperature: 5 days

Fridge: 7 days @ 2-8°C

Freezer: 30 days @ -20°C

Cause for Rejection

Specimen Acceptability and Transport Guidance

Instrument, Methodology

Roche cobas e 602, immunoassay

Test Availability

24 hours a day, 7 days a week

STAT Turnaround Time

1 hour

Routine Turnaround Time

3 hours

Reference Ranges

12 - 22 pmol/L

In case of discrepancies, always interpret results using reference ranges as stated on laboratory reports and/or electronic patient chart.

Laboratory Contact Information

416-586-4800 extension 4688