Total T4, or total thyroxine, is a blood test that measures the overall level of thyroxine, a primary hormone produced by the thyroid gland. Thyroxine plays a crucial role in regulating metabolism, growth, and development. Elevated levels can indicate hyperthyroidism, a condition where the thyroid gland is overactive. This can be due to Graves’ disease, thyroiditis, or taking too much thyroid hormone medication. Lower levels suggest hypothyroidism, where the thyroid gland is underactive. This can be caused by Hashimoto’s thyroiditis, thyroid removal, or certain medications.

Total T4 testing is commonly used to assess thyroid function, alongside other thyroid tests like TSH and Free T3, to diagnose and monitor thyroid disorders.