ABILITY OF 2 NEW THYROTROPIN (TSH) ASSAYS TO SEPARATE HYPERTHYROID PATIENTS FROM EUTHYROID PATIENTS WITH LOW TSH

We evaluated the ability of new thyrotropin (TSH) assays to separate h yperthyroid (n = 50) patients from clinically euthyroid subjects with low TSH values (nodular goiter, n = 20, and nonthyroidal illness, n = 22). Only patients whose serum TSH was <0.1 mIU/L by immunoradiometric assay were included. We used a new immunofluorometric method based on time-resolved fluorescence (TR-IFMA) and a new immunochemiluminometri c assay (ICMA) to measure TSH in serum. Although the differences betwe en the hyperthyroid patients and the euthyroid patients differed from each other by both methods (P = 0.0012 for TR-IFMA and P<0.0001 for IC MA), there was no cutoff point that could definitely separate the grou ps, Thus, it is not possible to draw any definite conclusions on wheth er a patient is hyperthyroid or not, solely on the basis of TSH concen tration measured with these new TSH assays.