Summary of Reasons for 131I DWBS− Tg+
| Reasons for 131I DWBS− Tg+ |
|---|
| False-positive Tg and true-negative 131I DWBS |
| Interference of circulating Tg Ab. |
| Benign lesions (possibly containing thyroiditis) of persistent residual thyroid tissue or nonthyroidal tissue producing Tg. |
| True-positive Tg and false-negative 131I DWBS |
| Defective iodine-trapping mechanism such as acquired inactivation mutation of NIS, TPO gene, and pendrin. |
| Dedifferentiation of tumor such that it can still produce Tg but has lost its iodine-trapping ability. |
| Dispersed microscopic metastases too small to be visualized. |
| Improper patient preparation before 131I DWBS such as stable iodine contamination and inadequate TSH elevation. |