Serum thyroglobulin levels in patients with well-differentiated thyroid cancer during suppression therapy: study on...

Serum thyroglobulin (Tg) was measured in 429 patients with well-differentiated thyroid carcinoma, during thyroid hormone suppression therapy. 324 patients out of 429 were considered free of disease; 44 had only remnants in the thyroid bed; 61 had metastases, of them 40 were detected by TBS and 21 were nonfunctioning and were detected by other diagnostic procedures. Tg was measured by a RIA method in 257 patients and by an IRMA method in 277 patients. The correlation between the two methods was very good (r = 0.914) for values higher than 25 ng/ml with the RIA method. The cut-off limit to distinguish pathological from nonpathological values was considered the mean value found in the patients free of disease plus 2SD. The cut-off limit for the RIA method was 24.2 ng/ml and 3.0 ng/ml for the IRMA method. Of patients with high Tg levels 92% had metastases, either nodal or distant; only 8% had remnants in the thyroid bed. Tg levels were high in 80% of the patients with metastases, all but two of the patients with metastases and low Tg levels had nodal metastases. Moreover, Tg levels were high in 76% of the patients with metastases unable to take up radioiodine.

patients with low levels of serum Tg during suppression therapy have a high probability of being free of disease, even though the presence of tumors cannot be excluded. On the other hand a value greater than the cut-off limit suggests the presence of metastases despite a negative scan.