Low TSH with normal T3 and T4 can be seen in subclinical hyperthyroidism, which may be caused by thyroxine replacement therapy, nodular goiter, Graves’ disease, etc. Subclinical hyperthyroidism is a specific type of hyperthyroidism in which serum thyroid hormone levels are normal but serum TSH is below normal. It can be seen in medical excess thyroxine replacement therapy, multinodular goiter, Graves’ disease, autonomous functional thyroid adenoma, occult thyroiditis, postpartum thyroiditis, thyroiditis caused by drugs such as amiodarone or interferon. When patients have low TSH and normal T3 and T4, they should consult a doctor in time to improve the examination and treat the symptoms.