The thyroid function test is usually done by intravenous blood sampling, before and after meals, and is not affected by food intake. It is usually performed during an endocrinology visit when thyroid disease is considered to be present. The five tests of thyroid function generally include thyrotropin TSH, free T3 and T4, and total T3 and T4. The results of the tests are used to determine whether hyperthyroidism, hypothyroidism and thyroid function are normal in order to clarify the type of thyroid disease. Due to the workflow, blood sampling time in general hospitals is mostly in the morning. If patients have to undergo other blood tests, such as liver function, there are restrictions on eating and blood sampling time, so it is recommended to arrange the examination time reasonably in combination with the requirements of other laboratory tests. In addition, it is important to eat a light diet three days before the blood draw, do not eat seafood foods such as seaweed, prohibit alcohol consumption, avoid mood swings, ensure sufficient sleep, do not stay up late, and do not exercise strenuously.