If tg is thyroglobulin, and thyroglobulin is elevated after iodine 131 treatment, radiological thyroiditis may exist; it may also indicate recurrence or persistent cancer foci of thyroid cancer. 1. Radioactive thyroiditis: radioactive thyroiditis may occur after iodine 131 treatment, and thyroglobulin in the thyroid tissue may be released into the blood, causing an increase in thyroglobulin. Patients may also have localized pressure and swelling of the thyroid gland, and T3 and T4 may be elevated. 2. Thyroid cancer with recurrence or persistent cancer foci: Thyroid cancer such as papillary thyroid cancer and medullary thyroid cancer, if thyroglobulin shows persistent elevation after iodine 131 treatment, it may suggest that the tumor has recurred, the cancer foci still exists or metastasis, etc. It is recommended to go to the hospital in time for medical consultation and treatment under the guidance of doctor. If thyroglobulin is elevated, it is recommended to consult the endocrinology department or thyroid surgery department of regular hospitals for preliminary evaluation, and firstly, to be alert to the possibility of malignant tumor cells in the thyroid gland.