Low FT4 is considered to be caused by hypothyroidism. FT4 is synthesized and secreted by thyroid cells and has a very important role in maintaining body temperature, metabolism, heart rate, and protein, fat, and sugar metabolism. low FT4 can easily lead to hypothermia, chills, bradycardia, mucinous edema, memory loss, etc. The main cause of low FT4 is chronic thyroiditis, which can lead to a decrease in the ability of thyroid cells to synthesize and secrete FT4. can lead to a decrease in the ability of thyroid cells to synthesize and secrete FT4. Thyroid function is regulated by thyrotropin, and pituitary lesions, where the pituitary gland’s ability to synthesize and secrete thyrotropin is reduced, can further affect thyroid function, leading to a decrease in the ability to synthesize and secrete FT4 and inducing central hypothyroidism. After the diagnosis of hypothyroidism is confirmed, treatment with thyroxine tablets is required.