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HelpTest 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 FFT4F as an alternative. See test notification here.
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 |
|---|---|---|
| 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
CPT Code Information
84439
Report Available
3 to 8 daysReject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
Method Name
Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)
Secondary ID
8859Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.