Objective Serum thyroglobulin (Tg) is a marker of residual differentiated thyroid cancer (DTC) after total thyroidectomy; however, circulating antithyroglobulin antibodies (TgAb) may interfere with the immunoassay for Tg. Ultrasensitive assays may have a more significant role in detecting circulating Tg in the context of samples containing TgAb. The aim of this study was to evaluate the utility of ultrasensitive thyroglobulin (US-Tg) measurement compared to standard Tg measurement and to assess the influence of serum TgAb positivity on Tg detection in a large tertiary referral centre cohort in Australia.
Design All patients with DTC who had undergone total thyroidectomy were included in this retrospective, observational cohort study.
Patients Patients providing samples for the period of June 2006 until January 2014 were analysed. Three thousand two hundred and eight samples were measured at the same points in time, enabling serum Tg assays to be compared for the same TSH status (stimulated or suppressed).
Measurements The standard assay, the Siemens Immulite 2000 Tg assay, was compared to the serum ultrasensitive ELISA RSR (TM) Tg. TgAb were simultaneously measured using Abbott Architect or Immulite 2000.
Results There were 3019 samples included in the final analysis for comparison of the standard and ultrasensitive assays along with TgAb status. The majority of samples were TgAb negative (87%), with 48% of TgAb-negative samples associated with an undetectable serum Tg, suggestive of disease-free status at the time of sampling. Of note, 26% (n = 104) of the TgAb-positive samples were positive for Tg on the ultrasensitive Tg assay, but negative on the immulite Tg assay, and 62.5% (n = 65) of these samples corresponded to DTC recurrence.
Conclusion The US-Tg assay has greater clinical utility than the standard immulite Tg assay specifically in the scenario of antibody positivity, with a significant number of samples corresponding to clinically relevant recurrent or metastatic disease.