T3, Free

T3, Free

Alternate Test Name

Free Triiodothyronine

Epic Mnemonic
Sunquest Mnemonic

LAB137
FT3

Category

Chemistry

Methodology

Electrochemiluminescence immunoassay

Test Performance Schedule

Sunday - Saturday

Result Availability

Within 24 hours

Container

Gold top (SST), Red top (serum), or Green top (lithium heparin) tube

Volume

Pref. Vol.: 1.0 mL serum or plasma
Min. Vol.: 0.5 mL serum or plasma

Collection Instructions

• Routine venipuncture

• Immediately after collection, gently invert tube 5-10 times

• Clot 30 minutes

• Promptly centrifuge 10 minutes

• If no gel barrier is present immediately transfer serum or plasma to a plastic tube and refrigerate

• Properly centrifuged gel barrier tube does not require transfer of serum or plasma to separate tube

Transportation Instructions

Refrigerated

Stability

• Refrigerated: 5 days

Remarks

Biotin, also referred to as Vitamin B7 or Vitamin H, can interfere with this test when taken in mega doses of 5mg (5000 mcg) or more. It is often promoted as a skin and hair beauty aid. Please ask your patients to refrain from taking Biotin or supplements containing Biotin for at least 24 hours before collecting specimens for lab testing.

https://biotinfacts.roche.com/

https://www.fda.gov/medicaldevices/safety/alertsandnotices/ucm586505.htm

CPT Codes

84481

Effective/Revised

03/30/2017

The thyroid hormones triiodothyronine (T3) and thyroxine (T4) are secreted into the bloodstream by the thyroid gland and play a vital role in regulating the body’s metabolic rate, influencing the cardiovascular system, growth and bone metabolism, and are important for normal development of gonadal functions and nervous system.

T3 circulates in the bloodstream as an equilibrium mixture of free and serum bound hormone. Free T3 (fT3) is the unbound and biologically active form, which represents only 0.2-0.4 % of the total T3. The remaining T3 is inactive and bound to serum proteins, while the distribution of T3 between these binding proteins (thyroxine binding globulin, pre-albumin, albumin) is controversially discussed.

The determination of free T3 has the advantage of being independent of changes in the concentrations and binding properties of the binding proteins; additional determination of a binding parameter (T-uptake, TBG) is therefore unnecessary. Therefore free T3 is a useful tool in clinical routine diagnostics for the assessment of the thyroid status. Free T3 measurements support the differential diagnosis of thyroid disorders, are needed to distinguish different forms of hyperthyroidism, and to identify patients with T3 thyrotoxicosis.