Name: TSH Reflex Free T4
Test Name: TSH Reflex Free T4
Health Link Test Code: TSHT4
LIS Test Code: TSHT4
CPT Code(s): 84443, 84439
Free T4 will be performed if the TSH is <0.35 uIU/mL or >4.94 uIU/mL.
Methodology: Chemiluminescent Immunoassay
Days Performed: Daily, 24 hours.
In-Lab Turnaround Time: 4 hours.
Stat In-Lab Turnaround Time: 1 hour.
Collection Container: Green cap with yellow ring (PST)
Also Acceptable: Green top, Red cap with yellow ring (SST), Red top
Collection Volume: 1 mL
Pediatric Collection Volume: 0.5 mL
7 days if removed from cells, clot or gel
24 hours if on gel
Sample Analyzed: Plasma or serum
Testing Volume: 0.5 mL
Pediatric Testing Volume: 0.2 mL
Centrifuge. If a complete barrier has not formed, transfer cell-free plasma/serum to plastic vial. Refrigerate.
Transport specimen to the laboratory. Transport with coolant pack if coming from clinic location.
Age 9 days and up: 0.35 - 4.94 uIU/mL
FT4 (if performed):
|30 days-11 months||0.89-1.70|
|1 year and up||0.70-1.48|
Interpretation Type: Reference Interval
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.