Synonyms
Free Triiodothyronine
Clinical Significance
A free or total T3 test is often part of a thyroid panel, a group of tests which are used together to evaluate thyroid health. Free T3 testing may be used to determine whether thyroid replacement therapy is effective. It can also help diagnose abnormalities of the proteins that bind thyroid hormones.
T3 measurements are typically used along with other thyroid function tests, like TSH and free and total T4, to evaluate how your thyroid is functioning. It is used to evaluate pituitary gland problems, to assess the severity and type of thyroid disease, and to monitor treatment for a thyroid condition.
Specimen
Serum
Stability
7 days at 4 to 8 °C
30 days at -20 °C
72 hours at ambient temperature
Reference Range
3.1 – 6.8 pmol/L
Interpretation
| TSH | FREE T4 | FREE OR TOTAL T3 | THYROID FUNCTION |
|---|---|---|---|
| Normal | Normal | Normal | Normal Thyroid Function |
| High | Normal | Normal | Subclinical Hypothyroidism |
| High | Low | Normal or Low | Primary Hypothyroidism related to the Thyroid gland |
| Low or Undetectable | Normal | Normal | Subclinical Hyperthyroidism |
| Low | High | High | Primary Hyperthyroidism related to the Thyroid gland |
| Low | Low | Low or Normal | Secondary Hypothyroidism related to the Pituitary gland |
| Normal or High | High | High | Secondary Hyperthyroidism related to the Pituitary gland |
Limitation
A number of factors can impact the free T3 level in the blood, including: Pregnancy, Disease and Medications.