Free T4
Ordering Info & Methodology
Test Code
Cerner Synonyms
FT4
Thyroxine Free, fT4, Free T4, Free T4 (Thyroxine), Free Thyroxine FT4, Non-Protein Bound Tetraiodothyronine, T4 Free, Thyroxine, Thyroid Function Cascade
Turn Around Time
Methodology
Analyzed within 1 day of receipt. Available on a STAT basis.
Competitive immunoassay, electrochemiluminescence, Roche Cobas
Ordering Guide
Specimen Requirements
Sample Type
Collection Container
Alternate Collection Containers
Serum
Gold
Red
1.0 mL
Seven days
Add on stability
This is the length of time after sample collection that this analyte is stable. Test can be added to a previously collected sample if the time since collection is less than the add on stability time.
Minimum Volume
Add On Stability
Collection and Shipping Requirements
Refrigerate. Send on ice pack.
Reference Intervals
Female Reference Interval
Age Category | Reference Interval | units |
|---|---|---|
0 y - <6 d | 11.0-32.0 | pmol/L |
6 d - <4 m | 11.5-28.3 | pmol/L |
4 m - <12 m | 11.9-25.6 | pmol/L |
12 m - <7 y | 12.3-22.8 | pmol/L |
7 y - <11 y | 12.5-21.5 | pmol/L |
11 y - <19 y | 12.6-21.0 | pmol/L |
≥ 19 y | 12.0-22.0 | pmol/L |
Male Reference Interval
Age Category | Reference Interval | units |
|---|---|---|
0 y - <6 d | 11.0-32.0 | pmol/L |
6 d - <4 m | 11.5-28.3 | pmol/L |
4 m - <12 m | 11.9-25.6 | pmol/L |
12 m - <7 y | 12.3-22.8 | pmol/L |
7 y - <11 y | 12.5-21.5 | pmol/L |
11 y - <19 y | 12.6-21.0 | pmol/L |
≥ 19 y | 12.0-22.0 | pmol/L |
Additional Notes
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Measurement Uncertainty (MU)
Every laboratory value is an estimate of the true concentration of substance. MU is the 95% confidence interval around that estimate. 95% of the time, the true concentration will be within the range of the reported value ±MU. This value is based on analytical variability (precision) and does not reflect other factors such as sample collection and handling which may also affect the result.
Example
Reported sodium = 140 mmol/L
Sodium MU = 1%
Expanded uncertainty = 140 mmol/L ± 1% or 140mmol/L ± 1.4 mmol/L
Interpretation - the true value of sodium in the sample is in the range 138.6-141.4 mmol/L, with 95% confidence.
7%
Measurement Uncertainty
When free T4 is ordered together with TSH, free T4 measurement will generally only be performed if TSH is abnormal.
Assay interferences are possible in patients taking high dose (>5mg/day) biotin supplementation.