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Laboratory Medicine

Test catalogue

Thyroxine, Free (Free T4)

Test Name

Thyroxine, Free (Free T4)

Gold Tube Specimen type/requirements

Container Type = 1 Gold Top (Adult) or 1 Green Top (Pediatric)

Minimum Volume = 3 ml Blood

Specimen Handling

Collection Instructions: Collect sample in gold top vacutainer(SST) for adult or 2mL green top vacutainer (lithium heparin) for pediatric samples. Ensure sample is well mixed. Write your initials, date and time of collection on the collection label or requisition.

Free T4 is ristricted to endocrinology, See choosing wisely guidelines for more instructions.

Write your initials, date and time of collection on the collection label or requisition.

Laboratory Staff Instructions: Only the endocrinology paper requisition has unrestricted access to ordering FT4, FT3. If you get the endocrinology paper requisition and FT4 or FT3 is ticked off, please order it. If you get any other paper requisition that says “FT4, FT3” on it (from any other location, including FHT or emergency), only order the TSH reflex test code. Do not order FT4 or FT3. The reflex will make sure that FT4 or FT3 is measured if TSH is abnormal.

Rejection Criteria: Grossly hemolyzed and icteric samples, Unlabeled or Not Sufficient Quantity samples will be rejected.

Stability: Sample is table for 8hrs at room temperature, 48hrs refrigerated, 1 month frozen at -20°C or lower.

Transportation: Send to Core Lab as soon as possible

Required Documentation

Turnaround Time (TAT)

1 Day

Test Utilization

FT4 will only be processed when TSH is abnormal

(Endocrinology has unrestricted access)

Reference Value

Therapeutic: 7.5 -16.0 pmol/L

Test Code



Chemiluminescent Immunoenzymatic Assay

Testing Location


Other Information