T4, Free

Test performed at York Hospital Laboratory.

Test Code

Alias/See Also
Free T4

CPT Codes

Preferred Specimen
0.2 mL serum collected in a serum separator tube (SST)

Other Acceptable Specimens
0.2 mL serum collected in a no additive (red-top) tube, transferred to a plastic screw-cap vial

Transport Temperature

Specimen Stability
Room temperature: 4 hours
Refrigerated: 7 days
Frozen: 4 weeks

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Plasma samples


Setup Schedule

Report Available
Next Day

Reference Range
Age Free T4 (ng/dL)
<=4 Days 2.18 - 5.28
1-4 Weeks 0.93 - 2.33
1-12 Months 0.78 - 1.79
1-5 Years 0.78 - 2.10
6-10 Years 0.81 - 2.10
11-19 Years 0.78 - 2.02
Adult 0.78 - 2.19

Clinical Significance
The FT4 concentration is believed to be the most direct indicator of an individual's thyroid status. FT4 concentrations are generally depressed in hypothyroidism and raised in hyperthyroidism. Measurement of FT4 thus provides an aid to the differential diagnosis of thyroid disease. FT4 concentrations are independent of the concentration of thyroid hormone binding proteins and may therefore be measured in patients with elevated or reduced binding protein concentrations without the need for additional tests of binding capacity.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.