ASSESSMENT OF THE INFLUENCE OF THYROGLOBULIN (TG) AUTOANTIBODIES AND OTHER INTERFERING FACTORS ON THE USE OF SERUM TG AS TUMOR-MARKER IN DIFFERENTIATED THYROID-CARCINOMA

The purpose of the study was to examine the value of a commercial immu noradiometric (IRMA) method for measuring serum thyroglobulin as a tum or marker after treatment for differentiated thyroid carcinoma, A pros pective analysis of consecutive serum samples from 53 patients was per formed using the IRMA method and a traditional double antibody radioim munoassay (RIA). The results were compared with those of 100 healthy c ontrol subjects and furthermore the method was validated by investigat ing sera from 24 patients with Hashimoto's thyroiditis positive for th yroglobulin autoantibodies. Finally, in vitro studies of the influence of thyroglobulin autoantibodies on the method were done, The IRMA met hod had an acceptable analytical precision and was more sensitive than the RIA. It was furthermore less sensitive to the presence of thyrogl obulin autoantibodies but it was affected by them, and it showed less unspecific serum effect, Both methods had limitations as tumor marker when the patients had a thyroid remnant, when serum thyrotropin was no t suppressed, and in cases of local recurrence, The highest predictive value was found in patients with distant metastases, Thus, in cases o f only slightly elevated serum thyroglobulin, the strongest indication for recurrence is still an increasing serum thyroglobulin level withi n the same patient rather than a single value.