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T4 Free

Test ID: 

704292

CPT code:

84439

Synonyms:

Thyroxine (T4), Free, Direct
Free T4, Direct, Serum
Free Thyroxine
T4, Free, Direct, Serum

Clinical Use:

Free T4 may be indicated when binding globulin (TBG) problems are perceived, or when conventional test results seem inconsistent with clinical observations. It is normal in subjects with high thyroxine-binding globulin hormone binding who are euthyroid (ie, free thyroxine should be normal in nonthyroidal diseases). It should be normal in familial dysalbuminemic hyperthyroxinemia.

Specimen Type:

Serum

Requested Volume: 

0.8 mL

Minimum Volume: 

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

Container Type: 

Red-top tube or gel-barrier tube

Patient Preparation: 

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.

Heparin has been reported to have in vivo and in vitro effects on free T4 assay. Hence samples should not be collected during or soon after the administration of this anticoagulant.

Collection:

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

Storage Instructions:

Room temperature

Stability Requirements:

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Rejection Criteria

Citrate plasma specimen; improper labeling

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