The five thyroid tests include total T3 and T4, free T3 and T4, and thyrotropin-releasing hormone, or TSH, and are used to check the function of the thyroid gland. This is usually seen after major thyroidectomy, where thyroid function is not secreted enough, resulting in decreased T3, T4, and free T3 and T4 and increased TSH. 3. It is also commonly used in subacute thyroiditis and chronic lymphocytic thyroiditis to determine thyroid function. If thyroxine is low, further thyroxine supplementation therapy is required.