The effect of 131I for diagnostic purposes on serum thyroglobulin (hTg) levels in subjects with thyroidal disorders.

The concentration of serum thyroglobulin was measured in sera of subjects with various thyroid disorders, before and after the administration of tracer doses of 131I. The mean serum human thyroglobulin (hTg) concentration before administration of the isotope was 35.2 ng/ml +/- 7.8 (SE) in 13 subjects and 36.3 ng/ml +/- 7.9 (SE) 24 h after the administration of 131I. The data indicate that no significant release of thyroglobulin occurs 24 h after the administration of tracer doses of 131I. In 2 of the 3 subjects, however, in whom samples were obtained at 4 and 8 h after diagnostic administration of 131I, a modest rise in serum Tg levels was observed. Determinations of serum thyroglobulin levels within 24 h after the administration of a tracer dose of 131I are nevertheless valid providing one allows sufficient time to elapse for tracer decay.