Sky-High Thyroglobulin Level Following Thyroid Lobectomy Without Evidence of Metastatic Disease

Thyroglobulin (Tg) serves as a crucial indicator for monitoring recurrence in patients with differentiated thyroid cancer following total thyroidectomy and radioactive iodine therapy. The utility of following Tg after thyroid lobectomy (TL) is debatable. There appears to be insufficient evidence to establish a specific Tg cutoff that can reliably detect persistent or recurrent disease after TL. The objective of this report is to describe a patient with an unexpectedly elevated Tg level following thyroid lobectomy for low-risk papillary thyroid carcinoma.

A 41-year-old female patient underwent a left thyroid lobectomy for low-risk classic papillary thyroid carcinoma. Her postoperative assessment reveals an unexpectedly elevated Tg at 4055 ng/mL (normal range: 3.5-77 ng/mL) with a negative Tg antibody <22 IU/mL (kIU/L). This is confirmed through repeated tests using multiple techniques to rule out laboratory errors and interference. Metastatic workup, including thyroid sonographic assessment and biopsy, chest computed tomography, and an 18F-fluorodeoxyglucose positron emission tomography scan, yielded negative results. Following thyroidectomy, the Tg level decreases dramatically to 0.7 ng/mL (0.7 μg/L).

Significantly elevated Tg levels after TL warrant careful consideration, but it is crucial to exclude potential laboratory errors and assay interference; additionally, it is essential to rule out underlying metastatic disease.

Measuring Tg and Tg antibody levels post-TL can provide a baseline for future reference. However, this case illustrates that high levels of Tg can be seen in the absence of thyroid cancer and therefore cannot reliably predict the risk of recurrence.