What is the Difference Between T3 and Free T3?
🆚 Go to Comparative Table 🆚The difference between T3 and Free T3 lies in their forms and how they are measured in blood tests. T3, or triiodothyronine, is a thyroid hormone that exists in two forms: bound and free. Bound T3 is attached to proteins, while free T3 is not attached to anything.
A total T3 test measures both bound and free T3 in the blood. It is considered a more reliable measurement than free T3 and is often used to diagnose hyperthyroidism or a pituitary gland disorder. The normal range for total T3 is 60 to 180 nanograms per deciliter (ng/dL).
A free T3 test measures only the amount of free T3 in the blood. It is generally less accurate than the total T3 test and is often used to determine whether thyroid replacement therapy is effective or to diagnose abnormalities of the proteins that bind thyroid hormones. The normal range for free T3 is 130 to 450 picograms per deciliter (pg/dL).
Both tests are typically used along with other thyroid function tests, such as TSH and free and total T4, to evaluate thyroid function.
Comparative Table: T3 vs Free T3
The difference between T3 and Free T3 lies in their bonding with proteins. T3, or triiodothyronine, is a thyroid hormone, and it exists in two forms: bound and unbound. Bound T3 is the form that is bonded with proteins, while Free T3 is the unbound form of T3. Here is a table summarizing the differences between T3 and Free T3:
| Feature | T3 (Bound) | Free T3 (Unbound) |
|---|---|---|
| Definition | Bound form of T3 with proteins | Unbound form of T3 |
| Existence | Most of the T3 in the bloodstream exists in this form | A small percentage of T3 exists in this form |
| Availability | Less readily available for use | Readily available for use |
| Measurement | Total T3 test measures both free T3 and bound T3 | Free T3 test specifically measures free T3 levels |
| Accuracy | Free T3 tests are generally less accurate than total T3 tests | |
| Thyroid Function | Both forms help control the body's metabolism, but free T3 is often considered a better indicator of thyroid function |
Both T3 and Free T3 can be tested to diagnose thyroid gland disorders, such as hyperthyroidism. However, free T3 is often considered a better indicator of thyroid function, as it can interact with the body's tissues.
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