Low correlation between serum thyroglobulin and 131I radioiodine whole body scintigraphy: implication for postoperative disease surveillance in differentiated thyroid cancer.

PURPOSE: To evaluate postoperative serum thyroglobulin (Tg) as a reliable tumor marker in low-risk differentiated thyroid cancer (DTC). METHODS: Two hundred and three patients met the selection criteria of >18 years old; who had undergone total or near total thyroidectomy; had a postoperative Tg, and had undergone 131I pre ablation whole body scan (PA-WBS). The primary endpoint was the correlation between Tg level and functional remnant thyroid tissues. Outcomes were categorized as concordant and discordant. Concordant results were positive Tg (>1 ng/ml) with positive PA-WBS or negative Tg (<1 ng/ml) with negative PA-WBS. Discordant results were negative Tg with a positive PA-WBS or positive Tg with a negative PA-WBS. To increase the sensitivity of Tg detection, we evaluated Tg in patients with high thyroid stimulating hormone (TSH) with serum level >30 mU/l on thyroxine withdrawal protocol. RESULTS: One hundred ten patients (54.1%) had discordant results (p < 0.05) with positive PA-WBS and Tg <1 ng/ml, while 93 patients (45.9%) had concordant results. For concordant results, 88 patients had positive PA-WBS and Tg >1 ng/ml, and 5 patients had negative PA-WBS and Tg <1 ng/ml. There was no patient with Tg >1 ng/ml and negative PA-WBS. There were 74 patients with high TSH (>30 mU/l) on abstention (thyroxine withdrawal protocol). Twenty-four (32.5%) had discordant results (p < 0.001) and 50 (67.5%) had concordant results. CONCLUSION: There is low correlation between postoperative Tg and PA-WBS. The sole use of Tg as a serum biomarker for postoperative disease status may not be reliable.