The Thyroxine (T4, Total), Serum test helps to evaluate the function of the thyroid gland, diagnose diseases of the thyroid, and monitor the effectiveness of ongoing thyroid treatment. It can also be used to diagnose congenital hypothyroidism in newborns sometimes. The Thyroxine (T4, Total), Serum test is done: • In case of signs and symptoms of thyroid disease • In case of enlarged thyroid • In case of thyroid nodule • After an abnormal result on a TSH test • For ongoing thyroid disorder treatment