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Test Code LAB127 T4, Free

Important Note

Note 1: If "TSH with reflex to Free T4 (FT4)" is requested, order TSH Cascade instead.

Note 2: This test is the replacement test for Free Thyroxine Index, T3 uptake, and Total T4 testing. 

Additional Codes

CPT Code: 84439

Performing Laboratory

TidalHealth Peninsula Regional - Core Laboratory: Chemistry

Specimen Requirements

Submit only 1 of the following specimens:

 

Plasma

Draw blood in a green-top (lithium heparin) tube. (Hemolyzed specimen is not acceptable.) Spin down and send 2 mL of lithium heparin plasma.

Note: 1. Indicate plasma.

2. Label specimen appropriately (plasma).

 

Serum
Draw blood in a gold-top serum gel tube. (Hemolyzed specimen is not acceptable.) Spin down and send 2 mL of serum.

Note: 1. Indicate serum.

2. Label specimen appropriately (serum).

Reference Values

0.92-1.68 ng/dL

Additional Information

TidalHealth has discontinued Total T4 testing. It is the opinion of our Department of Pathology that Total T4, whether ordered alone or in conjunction with a Free T4, does not aid in patient management. If a Total T4 is ordered, our laboratory will automatically convert the order to a Free T4. If a Total T4 is ordered with a Free T4, only the Free T4 will be assayed and reported. If a physician is adamant about getting a total T4, they should speak with a pathologist. 

Methodology

Electrochemiluminescence immunoassay (ECLIA)