What does it mean when only the thyroid-stimulating hormone (TSH) is elevated in the “three thyroid function tests,” while the other two parameters are normal?

　　Elevated thyroid-stimulating hormone (TSH) levels with otherwise normal thyroid function tests indicate subclinical hypothyroidism, which may result from autoimmune thyroiditis, excessive iodine intake, or antithyroid medications. A detailed analysis follows:

　　1. Autoimmune thyroiditis—including Hashimoto’s thyroiditis and atrophic thyroiditis—can lead to subclinical hypothyroidism.

　　2. Excessive iodine intake may induce latent thyroid dysfunction and can trigger or exacerbate autoimmune thyroiditis, resulting in hypothyroid symptoms.

　　3. Antithyroid drugs such as methimazole and propylthiouracil—used to treat hyperthyroidism—may cause thyroid damage, thereby precipitating subclinical hypothyroidism.

　　The normal reference range for TSH is 0.24–4.2 mIU/L. Diagnosis of subclinical hypothyroidism requires repeat measurement of thyroid function tests at intervals of 2–3 months. If clinical symptoms are present, prompt consultation with an endocrinologist is advised. Treatment with levothyroxine tablets should be initiated under the guidance of a qualified physician.