Test ID: Z0955
CPT code: 84439
LOINC: 6892-4
Specimen Type: Red, SST, OR Lav (EDTA) tube
Frequency: 6 – 11 days
Instructions: 1.0 mL Serum or Plasma from Red,SST,OR Lav-top(EDTA)tube, Frozen, Separate within 45 minutes. Min 0.5 mL; Pediatric Volume: 0.4 mL.
Text: Free thyroxine is the unbound portion of thyroxine that is biologically active and used along with TSH to assess thyroid function. This assay provides enhanced accuracy over commonly used automated testing methods and is not affected by clinical conditions that may impact protein –binding capacity.
Methodology: Direct dialysis mass spectrometry; high pressure liquid chromatography/mass spectrometry (HPLC/MS)