Influence of thyroid substitution therapy and thyroid autoantibodies on the value of serum thyroglobulin in recurring thyroid cancer

The study was performed to evaluate the influence of thyroxine substitution therapy and the presence of thyroglobulin antibodies (TgAb) on the usefulness of serum thyroglobulin (Tg) measurements in the follow-up of patients treated for well differentiated thyroid carcinoma. Seventy-two consecutive patients with differentiated thyroid cancer and eight with medullary carcinoma as well as controls were studied on one or more occasions and blood was drawn for measurement of serum Tg, TgAb, TSH and thyroid hormones. In 23 patients the hormonal substitution was withdrawn and 3-4 weeks later new blood samples and a 131I scintigraphy was performed. Eighteen patients were shown to have recurrence or metastases. Four of these had TgAb, two had normal Tg values, and the remaining 12 had extremely elevated levels. Those with TgAb and normal Tg values all had high Tg levels off thyroxine substitution. The 54 patients without evidence of recurrence had low levels of serum Tg except for one with highly elevated values. Based on the results from this and other studies is concluded that serum Tg is an important adjunct in the follow-up of patients with well differentiated thyroid carcinoma, but certain limiting factors have to be taken into account, i.e., the radicality of surgery, the sufficiency of the substitution, the presence of TgAb and the method for measurement of Tg.