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HelpTest Code FRT4D T4 (Thyroxine), Free, Dialysis, Serum
Test Down Notes
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Reporting Name
T4 (Thyroxine), Free by Dialysis, SUseful For
Determining thyroid status of sick, hospitalized patients
Determining thyroid status of patients in whom abnormal binding proteins have been identified
Possibly useful in pediatric patients
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumOrdering Guidance
The routine free T4 is faster and provides useful information for most patients; order FRT4 / T4 (Thyroxine), Free, Serum.
Necessary Information
Include name and telephone number of contact physician
Specimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 2.6 mL
Collection Instructions:
1. Collect specimen immediately before next scheduled dose.
2. Within 2 hours of collection, centrifuge, and aliquot serum into a plastic vial.
Specimen Minimum Volume
1.2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 28 days | |
| Frozen | 21 days | ||
| Ambient | 7 days |
Reference Values
0.8-2.0 ng/dL
Reference values apply to all ages.
Day(s) Performed
Monday, Wednesday, Thursday
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
84439
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| FRT4D | T4 (Thyroxine), Free by Dialysis, S | 6892-4 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 8859 | T4 (Thyroxine), Free by Dialysis, S | 6892-4 |
Interpretation
All free hormone assays should be combined with thyrotropin measurements.
Free thyroxine (FT4) levels below 0.8 ng/dL indicate possible hypothyroidism. FT4 levels above 2.0 ng/dL indicates possible hyperthyroidism.
Neonates can have significantly higher FT4 levels. The hypothalamic-pituitary-thyroid axis can take several days or, sometimes, weeks to mature.
Clinical Reference
1. De Brabandere VI, Hou P, Stockl D, Thienpont LM, De Leenheer AP. Isotope dilution-liquid chromatography/electrospray ionization-tandem mass spectrometry for the determination of serum thyroxine as a potential reference method. Rapid Commun Mass Spectrom. 1998;12(16):1099-1103
2. Jain R, Uy HL. Increase in serum free thyroxine levels related to intravenous heparin treatment. Ann Intern Med. 1996;124(1 Pt 1):74-75
3. Stockigt JR. Free thyroid hormone measurement. A critical appraisal. Endocrinol Metab Clin North Am. 2001;30(2):265-289
4. Sakai H, Nagao H, Sakurai M, et al. Correlation between serum levels of 3,3',5'-triiodothyronine and thyroid hormones measured by liquid chromatography-tandem mass spectrometry and immunoassay [published correction appears in PLoS One. 2016;11(7):e0159169]. PLoS One. 2015;10(10):e0138864.doi:10.1371/journal.pone.0138864
5. Kahric-Janicic N, Soldin SJ, Soldin OP, West T, Gu J, Jonklaas J. Tandem mass spectrometry improves the accuracy of free thyroxine measurements during pregnancy. Thyroid. 2007;17(4):303-311.doi:10.1089/thy.2006.0303
Report Available
3 to 8 daysMethod Name
Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)