The Thyroxine (T4) Blood Test from Walk-In Lab is a thyroid function test. It measures the level of thyroxine in the blood, helping to diagnose thyroid disorders such as hyperthyroidism and hypothyroidism.The Thyroxine Blood Test is also known as T4 total and Tetraiodothyronine. Patients should do not need to fast before taking the test and results are delivered within one to two days. A blood test from Walk-In Lab is a convenient, cost-effective and confidential alternative for those without a doctor’s order or without insurance.A T4 blood test assesses thyroid function by measuring the level of thyroxine in the blood. Decreased levels of T4 are typically found in hypothyroidism and in the third stage of(painful)subacutethyroiditis.Increased T4 is associated with hyperthyroidism, subacute thyroiditis in its first stage, and with thyrotoxicosis due to Hashimoto disease. A Thyroxine blood test can also be used to diagnose T4 toxicosis. Increased thyroxine can be caused by excessive intake of iodineorwithsurreptitioususeofthyroxine.Further, T4 levels may beabnormalinthepresenceofsystemicnonthyroidaldisease.Alterations in binding capacity or quantity of TBG can both increase and decrease total thyroxine without causing symptoms. Liver disease is a common cause of elevated T4 in nonthyroidal disease. Serum thyroxine and free thyroxine index (FTI) are increased in familial dysalbuminemic hyperthyroxinemia, a euthyroid syndrome where an abnormal binding site has affinity for thyroxine. Because T3 and T3 uptake (THBR) are typically normal in this entity, a T3 uptake blood test is commonly ordered alongside a T4 blood test.