Post-Thyroidectomy Radioactivity Uptake < 0.2% Predicts Unmeasurable Thyroglobulin After Total Thyroidectomy for Differentiated Thyroid Carcinoma
Postoperative radioactive iodine imaging often shows residual thyroid tissue in the operative bed after total thyroidectomy for differentiated thyroid carcinoma. In a single-institution study reported in JAMA Otolaryngology Head & Neck Surgery, Holsinger et al found that radioactive iodine uptake < 0.2%, found in approximately 4 of 10 patients, was significantly predictive of unmeasurable serum thyroglobulin after total thyroidectomy.
The study involved 245 patients undergoing total thyroidectomy for clinically staged cT1-3, N0, M0 differentiated thyroid cancer who underwent diagnostic postoperative radioactive iodine imaging at The University of Texas MD Anderson Cancer Center from January 2001 to February 2012. On the basis of quantitative measurements, radioactive iodine uptake in the thyroid bed of 0.2% of administered activity was selected as the cutpoint for presence or absence of thyroid remnant.
Association With Unmeasurable Thyroglobulin
On postoperative imaging, radioactive iodine uptake was < 0.2% in 106 patients (43%), whereas 139 (57%) had measurable iodine-avid thyroid tissue or tumor in the thyroid bed (n = 117, 84%), the neck (n = 4, 3%), or both (n = 18, 13%). Among all patients, the mean 24-hour radioactive iodine uptake was 0.62%. Assessment of stimulated serum thyroglobulin in 232 patients showed measurable levels (≥ 1 ng/mL) in 26 (25%) of 102 patients without thyroid remnant (radioactive iodine uptake < 0.2%) and in 87 (65%) of 133 with thyroid remnant (P < .001).
The investigators concluded, “A goal of postthyroidectomy [radioactive iodine uptake] of less than 0.2% helps maximize the likelihood of an unmeasurable postoperative [thyroglobulin] level, potentially simplifying follow-up evaluation and reducing the use of postoperative [radioactive iodine] in order to facilitate surveillance.”
F. Christopher Holsinger, MD, of Stanford University School of Medicine, is the corresponding author for the JAMA Otolaryngology Head & Neck Surgery article.
The study authors reported no potential conflicts of interest.
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