Laboratory: Clinical Biochemistry
Test Name:
TRIIODOTHYRONINE, FREE (Free T3) - (P)
Test Code: FT3
Clinical Information:
Free T3 is available as a component of the Thyroid Reflex Testing protocol.
Free T3 will be performed when TSH < 0.09 mU/L

Test Indications: This test is used in the second or third level evaluation of thyroid function in conjunction with TSH & free T4. Free T3 is the unbound and biologically active form & represents only 0.3% of total circulating T3.
Patient Preparation Instructions:  Multivitamins (45–125 µg biotin) or biotin-only supplements up to 1 mg per day do not interfere with this test. Samples should not be taken from patients receiving therapy with high biotin doses (i.e. >5 mg/day) until at least 8 hours after the last dose.
For additional information see:
Collection Devices:
Specimen Required:


Plasma: 2.0 mL

Stability 7 days refrigerated, 1 month frozen
Referral:
Serum: 2.0 mL

Samples must be transferred to an aliquot tube and stored frozen if analysis will not be complete within 48 hours (#110-10-05 Serum / Plasma Separation Procedure & Transport)
Requisition:
Reference Values:
0 - 7 d: 2.2-7.4   pmol/L                 
8d - 4 wk: 2.2-8.4
5 wk - 12 mo: 3.1-10.6
13 mo - 5 y: 3.7-10.3
6 - 10 y: 4.4-9.2
11 - 15 y: 4.8-9.1
16 - 20 y: 5.4-8.8
≥ 21 y: 3.7-6.9
Availability:
Daily
See Also:
More Information:
Free T3 is automatically performed when TSH < 0.09 mU/L except for ENDO, ENDM. Separate plasma and refrigerate.