Thyroxine, otherwise known as T4, is a hormone produced and secreted by the thyroid gland. At the tissue level, T4 is converted into the more active form of the hormone called T3. For this reason, T4 is considered a measurement of total production of thyroid hormone.

Hypothyroidism is a condition where T4 blood levels are low. This causes cellular dysfunction and metabolic breakdown. Symptoms may include weight gain, constipation, dry skin, and hair loss. Low T4 levels may even lead to the development of chronic diseases such as heart disease and diabetes.

Hyperthyroidism is the term for elevated T4 blood levels. Symptoms can include anxiety, insomnia, heart palpitations, and bowel discomfort.

Instructions

Fasting is not required for this test. Take all medications as prescribed.

Note

For a more extensive evaluation of thyroid function, Life Extension® offers a Comprehensive Thyroid Panel.