Test Code FRT4D T4 (Thyroxine), Free, Dialysis, Serum
Ordering Guidance
The routine free T4 is faster and provides useful information in most patients; order FRT4 / T4 (Thyroxine), Free, Serum
Necessary Information
Include name and telephone number of contact physician.
Specimen Required
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 2.6 mL
Collection Instructions:
1. Draw blood immediately before next scheduled dose.
2. Centrifuge and aliquot serum into plastic vial within 2 hours of collection.
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
SerumSpecimen 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.
Day(s) Performed
Monday, Wednesday, Thursday
Report Available
3 to 8 daysPerforming Laboratory

Test Classification
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test 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 |