If the FT4 level decreases and the TSH level increases, hypothyroidism should be considered. However, to confirm the diagnosis of hypothyroidism, the patient’s symptoms should be evaluated in addition to the patient’s thyroid function indicators. Elevated TSH is often indicative of primary hypothyroidism, i.e. hypothyroidism caused by a lesion in the thyroid gland itself, which is commonly associated with Hashimoto’s thyroiditis, iodine-131 therapy for hyperthyroidism, or hypothyroidism after surgery for hyperthyroidism. treatment. Unless it is a transient hypothyroidism, such as subacute thyroiditis, it can cause transient hypothyroidism, in which case no treatment is needed, so clinical attention should be paid to differentiation.