Preferred Sample Type
Suitable Specimen Types
- Serum
Sample Processing in Laboratory
Usual
Sample Preparation
Centrifuge
Turnaround Time
1 daySample Stability
Serum and Lithium, Sodium, EDTA, Sodium Citrate, Sodium fluoride/oxalate Plasma.
Store at 4 ºC for up to seven days. For longer periods store at -20 ºC.
Free T4 (FT4) Thyroxine
General Information
The thyroid hormone T4 is physiologically part of the regulating circuit of the thyroid gland and has an effect on the general metabolism. The major fraction of the total thyroxine is bound to transport proteins (TBG, prealbumin, and albumin). The free thyroxine (fT4) is the physiologically active thyroxine component.
The determination of free thyroxine is an important element in clinical routine diagnostics. Free T4 is measured with TSH when thyroid function disorders are suspected. The determination of fT4 is also suitable for monitoring thyrosuppressive therapy. The determination of free T4 has the advantage of being independent of changes in concentration and binding properties of the binding proteins.
Patient Preparation
Patients receiving therapy with biotin (> 5mg/day) should not have samples taken for analysis until at least 8 hours post dose.
Patients receiving treatment with lipid lowering agents containing D-T4 should have the treatment suspended 4-6 weeks prior to FT4 measurements.
Notes
FT4 is usually performed only after laboratory reflex consideration of first line TSH analysis. Auto-antibodies to thyroid hormones can interfere with the assay.
Trimester-specific reference ranges for thyroid function:
|
Abbott reference range |
Trimester 1 |
Trimester 2 |
Trimester 3 |
|
|
TSH (mIU/L) |
0.4 - 4.9 |
0.0878-2.8293 |
0.1998-2.7915 |
0.3070-2.9028 |
|
FT4 (pmol/L) |
9 - 19 |
10.53-18.28 |
9.53-15.68 |
8.63-13.61 |
|
FT3 (pmol/L) |
2.9 – 4.9 |
3.52-6.22 |
3.41-5.78 |
3.33-5.59 |
Reference Range
Adults: 9 - 19 pmol/L
(Source: Abbott Diagnostics)
Specifications
- EQA Scheme?: Yes
-
EQA Status:
NEQAS and WEQAS