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Free T4
(a.k.a FT4)
minimum sample volume required ~ 5ml
Test Code: FT4
Tube type: SST
Other acceptable tube types
Lithium heparin (pale green)
Special instructions
None
Reference Range
0 - 14 days: 17.0 - 57.0
15 days - <3 years: 9.5 - 17.8
3+ years: 8.0 - 18.0
Time limit for add on
3 days post collection
Units
pmol/L
Turnaround Time
2
days
Department: Biochemistry
Clinical Application
For the diagnosis and management of thyroid disease. FT4 analysis is automatically added by the laboratory when the TSH is above the reference range in patients not on thyroxine and when clinical details indicate FT4 analysis is appropriate e.g. hypopituitarism or pregnancy. .....................................................................................................................................................................
Test limitations: On rare occasions, this immunoassay may be subject to interference e.g. due to patient-specific endogenous anti-reagent antibodies. This assay is susceptible to positive interference from high levels of biotin. If biotin interference is suspected, TSH is a better marker of thyroid function (as the assay is not susceptible to biotin interference). It is recommended that biotin use is discontinued prior to blood collection. Please contact the duty biochemist if you wish to discuss any results that do not appear to be consistent with the clinical picture (01225 824050).
Webpage updated: October 2024.
