"Delfia" and "Amerlite": two sensitive nonisotopic immunoassay systems for assay of thyrotropin compared

We assessed the LKB "Delfia" (time-resolved dissociation-enhanced lanthanide fluoroimmunoassay) and the Amersham "Amerlite" (enhanced luminescent immunometry) assays of thyrotropin in serum. Both assays are sensitive (respective detection limits: 0.02 and 0.04 milli-int. unit/L) and have very good within- and between-batch precision over a wide range of thyrotropin concentrations. Results by the two methods correlate well (r = 0.992); the regression equation is: Amerlite = 0.915 Delfia - 0.33 milli-int. unit/L. The standard curve for the Delfia assay was linear, but that for the Amerlite assay showed some deviation from linearity below 0.5 milli-int. unit/L. Both assays have a negative bias in comparison with radiolabeled immunoradiometric assays, as judged by results for samples from the Quality Assurance Scheme. Both assays discriminate well between hyper-, hypo-, and euthyroid subjects, and results for thyrotropin for most patients with nonthyroidal illness were within the euthyroid reference interval. Both assays are convenient to perform and are based on systems that provide a viable alternative to radioimmunoassay.