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