Thyroglobulin - what is the postoperative threshold for the suspicion of thyroid cancer recurrence in the absence of anti-Tg antibody measurement?

BACKGROUND: Thyroglobulin (Tg) is used as a postoperative marker for the follow-up of patients with thyroid carcinoma, but there is no consensus regarding the value that may indicate possible recurrence. Aim. To evaluate Tg levels as a marker for recurrence of thyroid carcinoma.

SUBJECTS AND METHODS: Demographics and survival of 80 patients who underwent total thyroidectomy for well-differentiated thyroid cancer were analysed and related to Tg levels. Tg measurements were performed when patients were euthyroid, after completion of treatment.

RESULTS: The median Tg value was 1.3 ng/ml. Higher values were found in males, high-risk patients and patients with recurrent disease. Using the median Tg value as cut-off, patients were divided into two groups (group I ≤1.3 ng/ml and group II >1.3 ng/ml). There was a significant correlation between values >1.3 ng/ml and recurrence. When survival was related to Tg values, there was a tendency towards worse prognosis in group II. The best predictive cut-off value for recurrence was found to be 1.3 ng/ml, which had a sensitivity of 77% and a specificity of 57%.

CONCLUSIONS: Although low, a cut-off Tg level of 1.3 ng/ml represents a simple indication for further investigation in patients receiving thyroxine after completion of treatment for thyroid cancer, in the absence of measurement of anti-Tg auto-antibodies.