Quantitative evaluation of hormonal extraction performed by continuous plasma exchange in euthyroid patients. Application to the treatment of severe hyperthyroidism

: Plasma exchanges (PE) have been successfully used in the treatment of thyroid storm. The dramatic results obtained (as in the case reported here) have prompted the authors to evaluate the effects of PE on plasma thyroid hormone (T4, T3 and unbound T4) levels and thyroxine-binding globulin (TBG) levels in 5 euthyroid patients. PE of one blood volume consistently produced a significant decrease in T4, T3 and TBG levels without changes in unbound T4 or TSH. Hormone extraction was proportional to the volume of blood removed and correlated with the amount of TBG extracted. Compared with the estimated total plasma content, the percentage of unbound T4 extracted was superior to that of total T4, which suggests release of free hormones from the intracellular compartment. Repeated PE in the same patient resulted in a transient decrease in T4 without changes in TSH. These results indicate that PE constitutes a fast, simple and effective means of removing thyroid hormones in all emergencies related to thyrotoxicosis. The fact that TSH levels remain stable after PE shows that the thyroid balance in euthyroid subjects is unaffected by this method.