Feb 8, 2018




Clinical Hub,Tools & Resources,UWHC Lab Test Directory,Chemistry

TSH Reflex Free T4

TSH Reflex Free T4 (TSHT4) Chemistry Lab Test

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

Test Component:


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.

Specimen: Blood

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

Stability Refridgerated:

7 days if removed from cells, clot or gel

24 hours if on gel

Stability Frozen:

6 months

Sample Analyzed: Plasma or serum

Testing Volume: 0.5 mL

Pediatric Testing Volume: 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 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):

Age ng/dL
5-14 days 1.05-3.21
15-29 days 0.68-2.53
30 days-11 months 0.89-1.70
1 year and up 0.70-1.48

Interpretation Type: Reference Interval

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.