Evaluation of a time-resolved immunofluorometric assay for serum thyroid stimulating hormone

The LKB 'Delfia, immunofluorometric assay for serum TSH has been evaluated. The assay is simple and rapid to perform and is capable of processing in excess of 100 specimens within a working day. The sensitivity of the assay is 0.05 microU/L, with a working range extending beyond 324 microU/L. The change in signal at each point over the standard curve approaches 1000-fold, significantly greater than that of a typical immunoradiometric assay. Mean figures for intra-assay and inter-assay precision were 4.7% and 8.6% CV, respectively. Mean recovery of added TSH was 98.3%, and samples containing high levels of endogenous TSH diluted parallel to the standard curve. The method showed good correlation with an immunoradiometric assay for TSH. The reference ranges for clinically defined groups of subjects were euthyroid 0.47-3.84 microU/L (n = 83); primary hypothyroidism 15--greater than 324 microU/L (n = 28); thyrotoxicosis less than 0.05 microU/L (n = 46). It is concluded that the 'Delfia' assay offers the clinical biochemistry laboratory an attractive and reliable alternative to a sensitive immunoradiometric assay for serum TSH.