A laboratory and clinical evaluation of an immunochemiluminometric assay of thyrotropin in serum.

We evaluated an immunochemiluminometric assay for human thyrotropin. A chemiluminescent acridinium ester is used as a label, with magnetic-particle separation. The lower limit of detection of the assay (mean + 3 SD of the zero standard) was 0.07 milli-int. unit/L, with a working range of 0.5 to greater than 60.0 milli-int. units/L. Assay accuracy was good as judged from analytical recovery, analysis of external quality-assessment samples, and comparison with an enzyme-amplified immunoassay. There were no significant interferences or cross-reactivities. Twenty-four samples assayed showed aggregation of the magnetic particles. On re-assay, four of these samples showed a significant increase in the measured TSH by the luminescence assay. Assay time for 60 tubes was approximately 3.5 h with the use of a semi-automated luminometer. The reference interval, determined from data on 144 healthy euthyroid subjects, was 0.3-4.0 milli-int. units/L. Sixteen of 19 thyrotoxic patients showed clearly suppressed concentrations of thyrotropin in serum.