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Test Code LAB0232348 T4 (Thyroxine), Free, Dialysis, Serum

Additional Codes

Mayo Test ID
FRT4D

Test Down Notes

This test is temporarily unavailable. For additional details see test announcement here.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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

Method Name

Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)

Reporting Name

T4 (Thyroxine), Free by Dialysis, S

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

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus Reject

Reference Values

0.8-2.0 ng/dL

Reference values apply to all ages.

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.

Day(s) Performed

Monday, Wednesday, Thursday

Report Available

3 to 8 days

Specimen Retention Time

2 weeks

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