Free T3 (FT3) - Free Triiodothyronine Lab Test

Clinical Definition of Free T3 (FT3) - Free Triiodothyronine

Triiodothyronine (T3) is a thyroid hormone vaulted to transporter proteins that circulate in the blood. the predominant transport protein is thyroxin binding globulin (TBG). The free (unbound) segment of triiodothyronine (free T3) is in control of the biological action and influences the body’s control of metabolism. Free Triiodothyronine test measures the amount of T3 in the blood. Blood levels of T3 are higher or lower because of inadequate or uncontrolled production of the hormone by the thyroid gland because of thyroid dysfunction or pituitary dysfunction. Abnormal levels of T3 in the blood are related tp hyperthyroidism, hypothyroidism, and slow metabolism.

When do you expect results?

24 to 36 Hours

Why Get Tested?

The FT3 is ordered to detect hyperthyroidism, to verify thyroid function and help analyze progress of a person with a thyroid disorder

Reason to take Free T3 (FT3) - Free Triiodothyronine Test

Symptoms generally observed are:

Excessive amounts of T3 in the blood results in symptoms associated with hyperthyroidism such as:

  • Nervousness
  • Tremors of the hands
  • Weight loss
  • Insomnia
  • Puffiness around dry, irritated eyes

Eyes cannot move normally Insufficient amounts of T3, show symptoms associated with hypothyroidism and a slowed metabolism, such as:

  • Weight gain
  • Dry skin
  • Fatigue
  • Constipation

Preparations Needed for Free T3 (FT3) - Free Triiodothyronine Test

Preparatory instructions before the test*:

No Fasting required.
No other special preparations required

Sample Required?

Specimen type: Serum (Blood Sample), 

Specimen collection procedure: Venipuncture - Collection of blood from a vein, usually from the arm.

Understanding results of Free T3 (FT3) - Free Triiodothyronine

Reference RangeInterpretation
1.4 to 4.4 pg/mlNormal

“* Reference ranges may vary between labs depending on instruments used and method of establishment of reference ranges"

References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3857600/
  2. https://labtestsonline.org/tests/free-t3-and-total-t3
  3. https://www.ncbi.nlm.nih.gov/pubmed/8319367
  4. https://medlineplus.gov/ency/article/003687.htm
  5. https://www.healthdirect.gov.au/thyroid-function-tests