Clinical Impact of Thyroglobulin (Tg) and Tg Autoantibody Method Differences on the Management of Patients with Differentiated Thyroid Carcinomas

Context: Changes in thyroglobulin (Tg) and/or Tg antibody (TgAb) methods can disrupt the serial monitoring of differentiated thyroid carcinoma (DTC) patients. Objective: This study compared Tg measurements made in TgAb-negative and TgAb-positive sera using four RIA and 10 immunometric assay (IMA) methods. Design: TgAb detection using a panel of 12 direct methods was contrasted with four Tg recovery tests. Sera from 110 normal euthyroid subjects (68 TgAb negative/42 TgAb positive) and 131 TgAb-negative DTC patients had Tg and/or TgAb analyses made by 10 laboratories in four countries. Euthyroid controls were used to compare Tg and TgAb ranges, sensitivities, and TgAb interference, whereas DTC patients were used to study Tg assay specificities, hook effects, and the influence of high Tg levels on TgAb measurements. Results: Tg methods had high between-method variability [47 ± 3% (±sem)] that was only marginally reduced by CRM-457 standardization (37 ± 3%). All methods had suboptimal sensitivity, and some fa...