What is thyroglobulin (Tg)? What does it mean?
Thyroglobulin (Tg) is synthesized by the thyroid gland and secreted into the bloodstream by both normal and cancerous thyroid cells. Therefore, serum Tg concentration reflects the total number of thyroid cells, their function and damage. Since both normal and cancerous cells can secrete Tg, this indicator does not discriminate between benign and malignant thyroid nodules.
Patients with thyroid cancer who have undergone total thyroidectomy or post-operative radioactive iodine therapy have had their thyroid cancer cells and normal cells destroyed, and their blood Tg decreases and eventually stabilizes at a low level, and if Tg is found to be significantly elevated again during follow-up, be alert to the possibility of cancer recurrence.
What are the results of postoperative testing?
Total thyroidectomy
Professional guidelines both nationally and internationally recommend that if you have had total thyroidectomy, you need to have your serum Tg and Tg antibody (TgAb) levels tested every 6 to 12 months. Patients at higher risk of recurrence also need to be monitored more frequently.
Patients with differentiated thyroid cancer who have had all of their thyroid gland removed and are on TSH suppressive therapy (ie, taking thyroxine tablets) with Tg levels below 1 ng/mL generally indicate no residual tumor or recurrence.
Doctors sometimes also look at Tg levels after giving TSH stimulation to determine tumor remnants or recurrence. It is now believed that a Tg greater than 2 ng/mL with a TSH stimulation greater than 30 milliunits/liter generally indicates the absence of tumor remnants or recurrence.
Incomplete thyroidectomy
In this subset of patients, residual thyroid tissue can continue to secrete Tg.
The current professional opinion is that persistent elevated postoperative serum Tg levels may indicate thyroid tissue growth or tumor recurrence and require further determination.
If serum Tg levels are suggestive of residual tumor or recurrence, your doctor will recommend that you complete a systemic workup as soon as possible to look for suspicious lesions.
Co-written by Dr. Tingting Zhang, Cancer Hospital of Fudan University