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Thyroxine, Free

Mnemonic

T4F

Synonym

Free Thyroxine, Free T4, FT4

Specimen Collection Requirements

Collect

Serum or Plasma, one 5.0 mL gold (SST), 7.0 mL red or 3.0 mL green (lithium heparin, PST) top tube

Supply Item Number - 101235 , 101192 or 147641

Handling

Allow serum to clot completely at room temperature (minimum - SST: 30 minutes, red top tubes: 60 minutes). Centrifuge and separate serum and plasma from cells ASAP. 

Preferred Volume

1.0 mL Serum/Plasma

Minimum Volume

0.5 mL Serum/Plasma (1.2 mL minimum whole blood draw)

Transport

Refrigerated (2-8°C)

Rejection Criteria

Grossly hemolyzed specimens

Stability

AFTER SEPARATION FROM CELLS: Room Temperature (18-26°C): 8 hours; Refrigerated (2-8°C): 4 days; Frozen (≤ -20°C): 2 months

Testing Information

Performed

7 days/week

Reported

24 hours

Method

Chemiluminescent Immunoassay

Reference Values

Reference Values

Age

Male and Females

0 – 6 days

2.30 – 5.60 ng/dL

6 days – 14 years

0.80 – 2.20 ng/dL

≥ 14 years

0.84 – 1.51 ng/dL

Comments

Legacy Laboratory Services has validated the use of lithium heparin plasma with this assay. Lithium heparin plasma has not been approved or cleared by the U.S. Food and Drug Administration (FDA) for use with this test. Legacy is authorized under Clinical Laboratory Improvement Amendments (CLIA) to perform high-complexity testing.

CPT Codes

84439

Last Updated: Thursday, February 11, 2021 10:36:33 PM


Client Services: 503-413-1234