Free Triiodothyronine T3
T3 or triiodothyronine is the active form of the thyroid hormone. T3 acts as a metabolic throttle for fueling all of the daily cellular functions. Free T3 is the unbound portion of T3 that is biologically active.
T3 or triiodothyronine is the active form of the thyroid hormone. T3 acts as a metabolic throttle for fueling all of the daily cellular functions.
Hypothyroidism is a condition where T3 blood levels are low. This condition causes cellular dysfunction and metabolic breakdown. Symptoms may include weight gain, constipation, dry skin, and hair loss. Low T3 levels may even lead to the development of chronic diseases such as heart disease and diabetes.
Hyperthyroidism is the term for elevated T3 blood levels. Symptoms can include anxiety, insomnia, heart palpitations, and bowl discomfort.
This test measures the amount of free T3 available to the tissues, or free T3. Many doctors believe that evaluating the levels of free T3 is the best indicator of thyroid function. For a more extensive evaluation of thyroid function, you can order the Comprehensive Thyroid Profile.
The total T3 test measures the concentration of triiodothyronine in the serum. The T3 is increased in almost all cases of hyperthyroidism and usually goes up before the T4 does. Thus T3 levels are a more sensitive indicator of hyperthyroidism than the total T4, and T3 levels are therefore preferred for confirming hyperthyroidism that has already been suggested by a suppressed TSH result. T3 assays are also useful for the differential diagnosis of T3 thyrotoxicosis, a variant of hyperthyroidism that manifests itself with abnormally elevated T3 and suppressed TSH levels, while T4 levels remain within euthyroid (normal) limits. In hypothyroidism, the T3 is often normal even when the T4 is low. The T3 is decreased during acute illness and starvation and is affected by several medications including Inderal, steroids, and amiodarone. This test measures both bound and free hormone. And only the free hormone is biologically active. Since free T3 accounts for only about 0.5% of the total T3, the measurement of free hormone is generally considered to provide the more reliable indication of true thyroid status. As noted above for T4 levels, anything which affects thyroid-binding globulin (TBG), or albumin will affect the total T3 levels.
- This test measures the amount of T3 not bound by proteins and available to the tissues, or free T3.
- Many doctors believe that evaluating the levels of free T3 is the best indicator of thyroid function
- Needed to determine the level of active thyroid hormone primarily responsible for regulating metabolism to fuel all cellular functions
- Reference Interval: 2.0−4.4 pg/ml (>19 yr old)
- Methodology: Electrochemiluminescence Immunoassay (ECLIA)
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