Test Code FT4 T4 (Thyroxine), Free, Plasma or Serum
Performing Laboratory
MaineGeneral Medical Center
Methodology
Chemiluminescent immunoassay
Specimen Requirements
Submit only 1 of the following specimens:
Preferred:
Plasma
Draw blood in a green-top (lithium heparin) tube(s). For pediatric specimen, draw blood in a green-top (lithium heparin) MICROTAINER(S)®. Spin down and send 1 mL of lithium heparin plasma refrigerated. Label specimen with patient’s name (first and last), date of birth, date and time of draw, phlebotomist’s initials, and as plasma.
Alternate:
Serum
Draw blood in a gold-top (serum separater) gel tube(s). Spin down and send 1 mL of serum refrigerated. Label specimen with patient’s name (first and last), date of birth, date and time of draw, phlebotomist’s initials, and as serum.
Moderately hemolyzed specimens are not acceptable.
Specimen stability:
8 hours at room temperature
2 days refrigerated at 2-8°C
Indefinitely when frozen at ≤ -20°C
Minimum volume: 1 mL
Day(s) Test Performed
Monday through Sunday
Reference Values
Adults: 0.76-1.46 ng/dL
Critical value (automatic call-back): >4.0 ng/mL
Test Classification and CPT Coding
84439