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Test Code LAB4666 T4 (Thyroxine), Free, Dialysis, Serum

Additional Codes

SQ: FRT4DM

MAYO: FRT4D

Test Down Notes

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

Method Description

The tandem mass spectrometry method utilizes an equilibrium dialysis technique to separate free thyroxine (FT4) from serum proteins, including protein-bound T4. An isotope of thyroxine (L-thyroxine-[thyrosine-ring-(13)C6]) is added to the dialysate and serves as an internal standard. A liquid-liquid extraction with ethyl acetate further purifies the dialysate. After being dried down and reconstituted, the remaining extract is injected onto the tandem mass spectrometer where it undergoes high-throughput liquid chromatography combined with an electrospray ion source.(Unpublished Mayo method)

Report Available

3 to 8 days

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus Reject

Method Name

Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)

Secondary ID

8859