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Test Code FRT4D T4 (Thyroxine), Free, Dialysis, Serum

Test Down Notes

Effective August 23, 2024:  This test is temporarily unavailable due to increased volume of testing requests.  The downtime is expected to be >30 days.  Order FFT4T as an alternative. See test notification here.

Reporting Name

T4 (Thyroxine), Free by Dialysis, S

Useful 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

Serum


Ordering 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 days

Method Name

Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)