4.4. Quality requirements of basal S-TSH assays in predicting an S-TSH response to TRH

Different variants of a solid phase TSH radioimmunoassay method (having optimal precision at different S-TSH levels) were investigated for their capability in predicting an S-TSH response to TRH from the basal S-TSH levels. Sera from 283 patients with, or suspected of having a thyroid disorder, were tested. There was a highly significant correlation between the basal S-TSH level and the increase of S-TSH after TRH for a group of individuals with normal S-TSH levels. The best discrimination of responders to TRH from non-responders was obtained with a TSH assay method with prolonged preincubation (144 h) of serum specimens and antibody. With this method assay of the basal S-TSH level was found to be useful in predicting an S-TSH response to TRH in untreated patients suspected of having hyperthyroidism. The assay offers a less expensive diagnostic alternative to the TRH test in this clinical situation. We demonstrated the effect of varying the weight of the ratio of false positive to false negative results on the optimal decision level. The basal S-TSH level should be measured by different variants of the assay method whether this is used in the diagnosis of hyper- or hypothyroidism.