Free Triiodothyronine (Free T3)
Free triiodothyronine (Free T3) is one of the thyroid function tests that measures the level of unbound or free triiodothyronine hormone in the bloodstream. This test evaluates the amount of active thyroid hormone available to the body’s tissues. Here’s how Free T3 is used to evaluate thyroid function:
- Thyroid function assessment: Free T3 levels provide important information about thyroid function, especially regarding the production and activity of thyroid hormones. Alongside other thyroid function tests like Free T4 and TSH, Free T3 levels help diagnose and differentiate various thyroid disorders.
- Hyperthyroidism: Elevated levels of Free T3 are often observed in hyperthyroidism, a condition characterized by an overactive thyroid gland. Hyperthyroidism can result in symptoms such as weight loss, rapid heart rate, anxiety, heat intolerance, and tremors.
- Hypothyroidism: In contrast, decreased levels of Free T3 may indicate hypothyroidism, which occurs when the thyroid gland does not produce enough thyroid hormones. Hypothyroidism can lead to symptoms such as fatigue, weight gain, cold intolerance, constipation, and depression.
- Monitoring thyroid treatment: Free T3 levels are monitored in individuals undergoing treatment for thyroid disorders, such as hypothyroidism or hyperthyroidism. Adjustments to thyroid hormone replacement therapy (e.g., levothyroxine) or antithyroid medications (e.g., methimazole) may be made based on Free T3 levels to achieve optimal thyroid function.
- Thyroid hormone conversion: Free T3 is the active form of thyroid hormone that exerts its physiological effects on tissues throughout the body. It is converted from thyroxine (T4) primarily in peripheral tissues. Measuring Free T3 levels helps assess the efficiency of this conversion process, which can be altered in certain conditions or due to medications.