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HelpTest ID 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.
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, SSpecimen 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
Performing Laboratory
Mayo Clinic Laboratories in Rochester
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 |