Skip to Content
UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: T4, Free

Test Code(s): FT4

CPT Code(s): 84439

Methodology: Chemiluminescent Immunoassay

Days Performed: Daily, 24 hours.

Turnaround Time: Stat: 1 hour.
Routine: 4 hours.


Specimen Requirements

Specimen: Blood

Collection Container: Preferred: Green cap with yellow ring (PST)
Also Acceptable: Green top, Red cap with yellow ring (SST), Red top

Collection Volume: Preferred: 2 mL
Pediatrics: 0.4 mL

Sample Analyzed: Plasma or serum

Volume Required: Preferred: 1 mL
Pediatrics: 0.2 mL

Specimen Processing: Centrifuge.  If a complete barrier has not formed, transfer cell-free plasma/serum to plastic vial.  Refrigerate.

Specimen Transport: Transport specimen to UWHC Core Laboratory (B4/220). Transport with coolant pack if coming from outreach location.

Stability: Refrigerated: 14 days
Frozen: 3 months


Interpretation

Reference Interval:

1 year and up: 0.70-1.45 ng/dL

Test Limitations:

Results may be affected if patient has developed Human Anti-Murine Antibodies (HAMA) due to exposure to murine based products.

Thyroid autoantibodies in human serum may interfere and cause falsely elevated Free T4 results.

Free Thyroxine  Free T4

Back to Lab Test Directory Index