Enhanced luminescence immunoassay: evaluation of a new, more sensitive thyrotropin assay

We measured thyrotropin (TSH) with an enhanced luminometric assay ("Amerlite"; Amersham International). The detection limit of the assay is 0.02 milli-int. unit/L. Within-assay precision was 6.7 and 7.8% at 3.77 and 12.1 milli-int units/L, respectively, and between-assay precision was almost identical, whether singleton or duplicate samples were assayed. TSH measured in 132 euthyroid subjects ranged from 0.06 to 4.13 milli-int. units/L (mean 1.52, SD 0.86). Similar concentrations were found in 20 healthy pregnant women and 19 of 20 healthy post-menopausal women (one of whom had undetectable TSH). In 17 patients with primary hypothyroidism, TSH concentrations ranged from 9.34 to greater than 200 milli-int. units/L; and in 53 of 59 patients with hyperthyroidism, TSH concentrations were undetectable, ranging in the remaining six from 0.03 to 0.06 milli-int. unit/L. Results for TSH in 28 patients stimulated with thyroliberin were consonant with the results of the thyroliberin test in 25 cases. Thus, for most patients, measurement of a basal TSH concentration evidently will predict their thyroidal status and also the response to thyroliberin, but a few will require additional tests of thyroid function.