The value of Tg, or thyroglobulin, which can be determined as a thyroid cancer recurrence, needs to be determined according to the patient’s specific situation. If the Tg value is tested while the patient is taking levothyroxine, as long as Tg > 1ng/ml, it indicates the presence of cancer cells in the patient’s body and the possibility of cancer recurrence can be considered. If the Tg value is tested under the state of levothyroxine discontinuation, and the TSH, i.e. thyroid stimulating hormone, value is elevated to more than 30 mU/L, and Tg > 2 ng/ml then it indicates the presence of thyroid cancer in the body, and there is a certain risk of recurrence. When patients have abnormal Tg values as mentioned above, it is recommended to keep a positive attitude and not to give up treatment, but to go to the oncology department or thyroid surgery department of regular hospitals for timely treatment.