Equivalent discrimination among states of thyroid function by immunochemiluminimetric and immunoradiometric determination of thyrotropin.

New immunochemiluminometric assays (ICMA) of thyrotropin (TSH) have been reported to facilitate the diagnosis of hyperthyroidism. To compare the accuracy of ICMA-TSH with that of a conventional immunoradiometric assay (IRMA-TSH), we examined 115 consecutive patients of a thyroid outpatient clinic. On the basis of complete thyroid-function testing, including thyroliberin tests, the untreated patients (n = 89) were subclinically hyperthyroid (n = 21), subclinically hypothyroid (n = 13), or euthyroid (n = 55). The receiver-operating characteristic (ROC) curve, used for comparing the TSH values obtained by these two methods, was shifted to the left for the IRMA-TSH. The area under the curve was greater for IRMA-TSH than for ICMA-TSH (0.984 vs 0.869, respectively), which suggests equal or better clinical performance of IRMA-TSH vs ICMA-TSH in discriminating between hyperthyroidism and euthyroidism. Both assays displayed similar clinical sensitivity/specificity for evaluating thyroid function in hypothyroid and treated patients. We conclude that the ICMA-TSH tested is not more accurate than an IRMA in distinguishing between hyperthyroidism and euthyroidism.