Specific measurement of cyclosporine concentrations in whole blood: radioimmunoassay and fluorescence polarization immunoassay compared

Abstract

Letters A 39-year-old woman with a 20-year history of hypothyroidism caused by Hashimoto thyroiditis had been managed adequately with oral thyroxun (T4), 200 mg/day, until a few months before referral, at which time she developed symptoms of hyperthyroidism. Her thyroid hormone proffle at the time of referral is shown in Table 1 (Sample 1). Her normal value for serum thyrotropin (TSH) concentration indicates that she was euthyreid but, because of the high serum triiodothyronune (T3) value, the daily oral doseof T4 was decreased to 100 mg. The serum thyroid tests were repeated four weeks later (Table 1, Sample 2): The decreased T4 and increased TSH show that the patient had become hypothyroid at this dosagé of T4 but the serum T3 concentration was still in the high normal range.