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Test Code T4F FREE T4 (FREE THYROXINE)

Methodology

Competitive Chemiluminometric Immunoassay

Useful for detecting the unbound “free” metabolically active fraction of thyroxine (T4). The free T4 value, combined with the thyroxine-stimulating hormone (TSH) value, gives a more accurate picture of the thyroid status in patients with abnormal thyroxine-binding globulin (TBG) levels such as those who are pregnant or those who are receiving treatment with estrogens, androgens, phenytoin, or salicylates.

Specimen Requirements

 

Submit only 1 of the following specimens:

 

Preferred:

Serum Gel Tube

Container/Tube: Serum gel tube(s)
Specimen Volume: 2 mL (minimum volume: 1 mL) of serum

Collection Instructions: Spin down within 4 hours of draw.

 

Alternate:

Plain, Red-Top Tube

Container/Tube: Plain, red-top tube(s)
Specimen Volume: 2 mL (minimum volume: 1 mL) of serum

Collection Instructions: Spin down within 4 hours of draw.

Day(s) Test Set Up

Monday through Friday

Reference Values

0.8-2.2 ng/dL

Critical value (automatic call-back):

<50 years: >7.0 ng/dL

≥50 years: >6.0 ng/dL

Performing Laboratory

Logan Health Medical Center-Chemistry

Test Classification and CPT Coding

84439

Specimen Transport Temperature

Ambient