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

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Turnaround Time: 2 - 3 days
CPT Code:

84436, 84442

Test Type: 2 mL Serum
Stability Time:

Temperature

Period

Room temperature

7 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Reference Range:

Thyroxine Binding Globulin ug/mL 13 - 39
Thyroxine (T4) ug/dL 4.5 - 12.0
T4-TBG Index 2.5 - 6.0

Overview:

Collection Details:

Collection 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.

Red-top tube or gel-barrier tube.

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

Refrigerate.