Thyroglobulin can be used clinically as a tumor marker for differentiated thyroid cancer and as an important monitoring indicator for postoperative patients with differentiated thyroid cancer, with normal values generally ranging from 5 to 40 μg/L. Elevated thyroglobulin can be caused by thyroid disorders such as hyperthyroidism, toxic nodular goiter, subacute thyroiditis and chronic lymphocytic thyroiditis, or by malignant tumors such as differentiated thyroid cancer. Therefore, whether thyroglobulin over 300 μg/L is serious or not depends on the clinical examination as well as the specific condition, and cannot be generalized. If thyroglobulin exceeds 300 μg/L, the thyroid gland function and thyroid ultrasound are assessed to be benign, and the value can gradually return to normal after correct and standardized treatment, but regular follow-up and review are required. If the patient’s thyroid function and ultrasound examination are abnormal and the pathological examination suggests the presence of thyroid cancer, the patient should pay high attention to the disease, which will gradually tend to become serious. In addition, for patients who have been diagnosed with differentiated thyroid cancer and treated with total thyroidectomy, if thyroglobulin is found to be more than 300 μg/L during regular monitoring, it indicates a more serious condition and is considered to be caused by recurrence or metastasis of thyroid cancer, and further treatment should be promptly performed.