Thyroxine (T4), Thyroxine-binding Globulin (TBG), and T4−TBG Index

CPT: 84436; 84442
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Synonyms

  • TBG, Thyroxine (T4), and T4−TBG Index

Special Instructions

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.


Expected Turnaround Time

2 - 3 days


Related Documents


Specimen Requirements


Specimen

Serum


Volume

2 mL


Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)


Container

Red-top tube or gel-barrier tube


Collection

If a red-top tube is used, transfer separated serum to a plastic transport tube.


Storage Instructions

Refrigerate


Stability Requirements

Temperature

Period

Room temperature

7 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3


Causes for Rejection

Plasma specimen


LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
004457 T4, TBG and T4-TBG Index 001735 Thyroxine Binding Globulin ug/mL 3021-3
004457 T4, TBG and T4-TBG Index 001149 Thyroxine (T4) ug/dL 3026-2
004457 T4, TBG and T4-TBG Index 011735 T4-TBG Index index 3027-0

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