Ordering Recommendation

Not recommended for routine thyroid disorder screening; for initial screening, refer to Thyroid Stimulating Hormone (0070145). 
Test includes Thyroxine, Total (T4) (3005978) and T Uptake (3005977). The preferred alternative to this test is Thyroxine, Free (Free T4) (0070138).

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Serum separator tube. Also acceptable: Lavender (K2EDTA or K3EDTA), pink (K2EDTA), or green (lithium heparin).

Specimen Preparation

Allow specimen to clot completely at room temperature. Separate serum or plasma from cells ASAP or within 2 hours of collection. Transfer 1 mL serum or plasma to an ARUP Standard Transport Tube. (Min: 0.5 mL)

Storage/Transport Temperature


Unacceptable Conditions

Grossly hemolyzed specimens.


After separation of cells: Ambient: 4 days; Refrigerated: 8 days; Frozen: 1 year


Quantitative Electrochemiluminescent Immunoassay




Within 24 hours

Reference Interval

Test Number
Reference Interval
  T Uptake 0.8-1.3 TBI
  Thyroxine, Total T4
Cord Blood 6.60-17.50 ug/dL
0-3 days 5.37-22.40 ug/dL
4-30 days 5.24-23.20 ug/dL
1-23 months 5.37-16.00 ug/dL
2-6 years 5.26-14.80 ug/dL
7-11 years 5.70-14.10 ug/dL
12-19 years 4.74-14.60 ug/dL
20 years and older 4.50-11.70 ug/dL

  Free Thyroxine Index Calc 4.8-12.7 ug/dL

Interpretive Data

Thyroxine, Free (FT4) (0070138) is the preferred test alternative for T Uptake and Free Thyroxine Index tests.

Compliance Category



FTI = Free Thyroxine Index

Hotline History


CPT Codes

84479; 84436


Component Test Code* Component Chart Name LOINC
3005979 T Uptake 74795-6
3005980 Thyroxine, Total T4 3026-2
3005981 Free Thyroxine Index Calc 32215-6
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • Free thyroxine index
  • FT4 index
  • FTI
  • T4 uptake
  • T7
  • Thyroxine index
Free Thyroxine Index Panel