DIFFERENTIATION OF POSTPARTUM THYROTOXICOSIS BY SERUM THYROGLOBULIN -USEFULNESS OF A NEW MULTISITE IMMUNORADIOMETRIC ASSAY

Destruction-induced thyrotoxicosis and Graves' thyrotoxicosis must be differentiated, since they are treated differently. To find a useful m arker, we examined serial changes in serum thyroglobulin (Tg) concentr ations in 20 patients with postpartum thyroid disease (9, euthyroid Ha shimoto's disease; 11, Graves' disease in remission in early pregnancy ). Serum Tg was measured by a new multisite immunoradiometric assay th at allows little influence of anti-Tg autoantibodies. Eight women deve loped destruction-induced thyrotoxicosis 1 to 4 months postpartum, 6 h ad relapse of Graves' thyrotoxicosis 2 to 4 months postpartum, and 6 r emained euthyroid, In destruction-induced thyrotoxicosis, serum Tg 2 m onths before the onset was 13.3 +/- 11.4 mu g/L, then clearly increase d 1 month before (34.5 +/- 31.9 mu g/L) and was even higher at the ons et of thyrotoxicosis (116.5 +/- 137.1 mu g/L). In contrast, serum Tg i ncreased only at the onset in Graves' thyrotoxicosis (from 25.9 +/- 25 .2 mu g/L I month before to 76.1 +/- 75.3 mu g/L at the onset,p < 0.05 ). There was no difference in serum Tg level at the onset between the two disorders. However, when data were expressed as the percent increa se from the level one month before, and the cut-off value were taken a t 150%, all 7 patients above the cut-off developed destruction-induced thyrotoxicosis, and 6 of 7 below had recurrent Graves' thyrotoxicosis . Thus, serial measurement of serum Tg is useful for the differentiati on of destruction-induced thyrotoxicosis from Graves' thyrotoxicosis a fter delivery.