Comparison of three immunoassay kits for serum thyroglobulin in patients with thyroid cancer

Objectives: This study describes the evaluation of performance of three immunoassay kits [Sanofi-Pasteur, IRMA, with five monoclonal antibodies; Wallac-Delfia, FIA, with double monoclonal antibodies; and Diagnostic Products Corporation (DPC), RIA, with polyclonal antibodies] for serum thyroglobulin in patients with thyroid cancer. Specific aims were (a) to recognize a method with minimal interference, by comparing analyte recoveries, from thyroglobulin autoantibodies (TgAb) that can be present in some thyroid cancer patient samples, (b) to correlate individual results with those from Mayo Medical Laboratories (MML) (current referred out assay service used by our Institute), and (c) to compare assay precision. Methods: In evaluating performance of the three immunoassays, procedures were followed as recommended by the respective manufacturers. Parallel comparison of the three immunoassays with the MML procedure was performed with thyroid cancer patient sera. Recovery studies utilized sera from 15 thyroid cancer patients, 4 Hashimoto's thyroiditis patients, and 1 Grave's disease patient. TgAb were also measured directly by an IRMA thyroglobulin antibody kit (Sanofi-Pasteur). Results: Among the randomly selected 20 samples assayed in parallel studies, low recoveries (<80%) were present in 2 samples by IRMA assay (Sanofi-Pasteur), 8 samples by FIA assay (Wallac-Delfia), and 10 samples by RIA assay (DPC). The majority of the low recovery samples contained high titers of TgAb. All three kits correlated well with the Mayo method. At the control-1 level (similar to 9.9 mu g/L by Delfia determination), both the IRMA kit (CV = 1.96%, n = 10) and FIA Kit (CV = 2.16%, n = 10) showed good within-run precision. Conclusions: In our hands, the IRMA Kit (Sanofi-Pasteur) demonstrated excellent precision, analyte recoveries, the least interference from TgAb, and good correlation with the Mayo Medical Laboratories procedure.