Comparative plasma thyroglobulin measurements with three non-cross-reactive monoclonal antibodies in metastatic thyroid cancer patients.

In 12 normal individuals and 25 patients with metastases of differentiated thyroid cancer, plasma thyroglobulin (Tg) concentrations were measured simultaneously with three immunoradiometric assays. Each of the three systems used a different, non-cross-reactive monoclonal Tg antibody as second antibody. In general, there was a very close correlation between the results of the three different systems in the cross-sectional study of the 25 cancer patients as well as in longitudinal follow-up studies in selected patients. The monoclonal antibody Tg 40 produced values about 30% higher than the two other systems. The difference was, however, not statistically significant owing to the large scatter. The monoclonal antibody Tg 13 appeared to be very sensitive to interference with thyroglobulin autoantibodies. In conclusion, the monoclonal antibodies against the three epitopes tested produced very similar Tg values in normal individuals and 25 patients with metastatic thyroid cancer; however, before more is known about epitope specificity of Tg autoantibodies and heterogeneity of tumour Tg, monoclonal antibodies should be used for routine measurements only with caution.