Clinical reevaluation of radioimmunological thyroglobulin (hTg) determination in follow-up of differentiated thyroid carcinoma

A reevaluation of the clinical value of radioimmunological thyroglobulin (hTg) determination during follow-up of differentiated thyroid carcinoma, in general, confirms our previous results already published in 1980 and 1981. A total of 163 patients with differentiated thyroid carcinoma, 53 with papillary and 110 with follicular carcinoma, was studied up to January 1984. 586 sera are included in this study. The differentiation of suspicious from nonsuspicious findings was found to be based upon a cut-off concentration of 10 μg/l. Pathological findings were associated with hTg concentrations above 20 μg/l. Diagnostic accuracy was calculated to be between 95 and 97%, sensitivity of the method in comparison to be radioiodine whole-body scan was 98 versus 83%, respectively, and specificity 94%. At first 5 false negative and 6 false positive hTg findings have been obtained. 7.6% of the patients demonstrated endogeneous hTg antibodies by Boyden test. 7.7% of Boyden test negative sera showed an unacceptable hTg recovery of worse than +- 50%, which was possibly due to endogeneous antibodies. Again, endogenous TSH was able to stimulate hTg secretion in the form of elevated levels, yet did not affect the clinical diagnosis. Examples of the behaviour of hTg levels during follow-up are demonstrated. Specifically, the cases with false hTg findings are discussed. Basically, the conclusions are the same as in 1980 and 1981: hTg determination is able to replace the routinely performed radioiodine whole-body scan during follow-up, if once residual thyroid tissue and metastases have been excluded by means of radioiodine and an optimal follow-up program is used. (orig.)