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HelpTest Code FRT4DM T4 (Thyroxine), Free, Dialysis, Serum
Additional Codes
| Mayo | FRT4D |
| Epic ID | LAB4666 |
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.
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 |
Transport refrigerated.
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Method Name
Equilibrium Dialysis/Tandem Mass Spectrometry (MS/MS)
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
Day(s) Performed
Monday, Wednesday, Thursday
Report Available
3 to 8 daysReference Values
0.8-2.0 ng/dL
Reference values apply to all ages.
CPT Code Information
84439