Ordering Recommendation

Not recommended for routine evaluation of thyroid disorders; preferred test is Thyroxine, Free (Free T4) (0070138). Useful to evaluate free thyroxine (FT4) status in individuals with protein-binding abnormalities. Some medications may induce transient changes in FT4 concentrations. This test is not recommended for patients currently receiving heparin treatment because FT4 concentrations may be falsely elevated.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Plain red or serum separator tube (SST).

Specimen Preparation

Separate from cells or gel ASAP or within 2 hours of collection. Transfer 2 mL serum to an ARUP Standard Transport Tube. (Min: 0.3 mL)

Storage/Transport Temperature


Unacceptable Conditions



After separation from cells: Ambient: 4 days; Refrigerated: 2 weeks; Frozen: 1 month


Quantitative Equilibrium Dialysis (ED)/Quantitative High Performance Liquid Chromatography-Tandem Mass Spectrometry


Sun, Tue, Thu


2-6 days

Reference Interval

Effective May 16, 2011

Free Thyroxine ng/dL
Age Female Male
25-30 weeks gestation 0.5-3.3 ng/dL 0.5-3.3 ng/dL
31-36 weeks gestation 1.3-4.7 ng/dL 1.3-4.7 ng/dL
Birth to 1 week 2.2-5.3 ng/dL 2.2-5.3 ng/dL
2-3 weeks 0.9-4.0 ng/dL 0.9-4.0 ng/dL
1-5 months 1.1-2.2 ng/dL 1.1-2.2 ng/dL
6 months-6 years 1.4-2.7 ng/dL 1.4-2.7 ng/dL
7 years-17 years 1.1-2.0 ng/dL 1.1-2.0 ng/dL
18 years and older 1.1-2.4 ng/dL 1.1-2.4 ng/dL
Pregnancy, 1st Trimester 0.7-2.0 ng/dL
Pregnancy, 2nd Trimester 0.7-2.1 ng/dL
Pregnancy, 3rd Trimester 0.5-1.6 ng/dL

Interpretive Data

Some medications may induce transient changes in FT4 concentrations. This test  is not recommended for patients currently on heparin treatment as FT4 concentrations may be falsely elevated.

Compliance Category

Laboratory Developed Test (LDT)


Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
0093244 Free T4 by Equil Dialysis-TMS 6892-4
* 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.


  • Direct Dialysis
  • FT4
  • T4, Free, Equilibrium Dialysis
Thyroxine, Free by Equilibrium Dialysis/HPLC-Tandem Mass Spectrometry