Abnormal thyroid function means that when thyroid hormones are tested, changes in hormone levels are found. Thyroid hormone tests consist of three main hormones, free thyroid hormone, free triiodothyronine, and thyroid stimulating hormone. For example, if free thyroid hormone and free triiodothyronine are elevated, then thyroid stimulating hormone levels should be reduced, which is a characteristic of hormonal changes in hyperthyroidism. Conversely, if free thyroid hormone and free triiodothyronine are decreased, then thyroid stimulating hormone levels should be significantly increased, which is a typical sign of hypothyroidism. Therefore, the exact condition of abnormal thyroid function should be determined by combining the specific values of thyroid hormone levels from laboratory tests.