Thyroglobulin TG part 2 What you need clinically
1.Serum TG depends on Iodine status,thyroid mass,TSH stimulation, and any injury. TG is higher in iodine deficient areas. TG is a good marker for iodine status.
2. TG is not a useful marker for adult hypothyroidism diagnosis.
3. A low TG is useful to diagnose thyrotoxicosis factitia.
4.TG can be useful in diagnosis of subacute thyroitis as the TG stays elevated for 1-2 years after the blood tests and symptoms resolve.
5. TG antibodies limit the TG use in Hashimoto’s unless the RIA assay is used.
6. Elevated TG before and decrease after a trial of LT4 suppression can be helpful in deciding if a goiter responds to decreased TSH suppression. The hieght of the TG correlates with the size of the goiter. TG decrease correlates with decrease in goiter size and nodule shrinkage after LT4 therapy.
7. Thyroid and pleural fluid cysts can be diagnosed by the presence of TG in the fluid.1 cc saline is used to collect the TG. Dual TG/PTH samples fro cysts can determine if the cyst is of parathyroid origin or thyroid.
8. TG needle washout from a suspicious neck lymph node along with cytology can diagnose metastatic thyroid cancer.
9. Use of serial basal TG measurements along with endocrine neck ultrasounds can improve the cancer followup.
10 Positive TGAb can be used as a surrogate tumor marker when it is present. Nodules are more likely to be malignant when there are TGAb in the serum.Disease free cancer patients will take 3 years to lose the antibodies. The assay methods problems do not allow changing assays on the same patient.
11.Long term serum TG monitoring is the cornerstone of post surgery cancer surveillance.
12. Pre-op serum TG can be changed by needle biopsy injury. TG must be drawn 2 weeks away from the biopsy.
13. Remnant thyroid can persist even after RAI/131.Serum TG can persist at 0.1-1.0 ng/ml range for years.
14 the basal TG at the same TSH level along with Ultrasound is the best cancer surveillance method in 2017.
15. 2017 finds a marked decrease in the use of RAI/131 for thyroid cancer. The basal TG without radiation therapy is remarkable stable over years at 0.1-1.0 ng/ml.
16 Dx whole body scanning with I/123 or 131 has low value in 2017.
17. Basal TG doubling time has limited use in only patients with high tumor burdens and serum TG >100 ng/ml. It is not an independent variable except in this group.
Dr.Carole Spencer of USC thyroid lab has been my go to expert on TG and most of this information is from years of association with her and her chapter in THYROID textbook by Werner and Ingbar.