Characterization of a new highly sensitive immunometric assay for thyroglobulin with reduced interference from...

Measurements of serum thyroglobulin (Tg) with sensitive immunoassays are of great importance for the management of patients with differentiated thyroid carcinomas. However, interference of circulating autoantibodies to Tg (hTgAb) hampers the usefulness of most assays. We have produced a panel of monoclonal antibodies (mAbs) selected to bind Tg in the presence of Tg autoantibodies and developed a sensitive immunoassay for Tg with minor interference by hTgAbs. The antibodies were characterized by cross-inhibition and immunoassay combination studies, as well as affinity estimation. The within-run and total imprecision of the assay were determined with 2664 samples in 60 separate runs. The most sensitive assay combination with superior protection against autoantibodies consisted of two solid phase mAbs and two tracer mAbs with distinct binding sites. The assay was linear and displayed a wide dynamic range up to 1342 μg/l with a functional sensitivity of 0.1 μg/l and a total imprecision of less than 10 %. There was good agreement between the new high sensitive immunofluorometric assay (IFMA) and two well-established Tg assays from Brahms Kryptor and Roche Diagnostics. Mean difference between the new IFMA and the Kryptor assay was 0.059 μg/l with a 95 % confidence interval of -0.032 to 0.151 μg/l, whereas the mean difference between the new IFMA and the Roche assay was -0.80 μg/l with a 95 % confidence interval of -1.24 to -0.35 μg/l.