High FT3 in 2-year-old children is not necessarily hyperthyroidism; mildly high FT3 may be a normal physiological phenomenon; high FT3 may also be caused by hyperthyroidism, Hashimoto’s thyroiditis, etc. FT3 is also known as free triiodothyronine, which is a sensitive indicator of thyroid function in vitro. FT3, also known as free triiodothyronine, is a sensitive indicator of thyroid function in vitro, and FT3 is not affected by thyroid-binding globulin, so it is of great significance and value in the diagnosis of hyperthyroidism, hypothyroidism, and monitoring of the condition. Mild elevation of FT3 can be seen in childhood, which is a normal physiological phenomenon related to the rapid growth and development of children and the active metabolism of the body. High FT3 can also be seen in hyperthyroidism, diffuse toxic goiter (Graves’ disease), and initial chronic lymphocytic thyroiditis (Hashimoto’s thyroiditis). Children as young as 2 years of age who present with high FT3 can go to the hospital and have their doctor make a determination.