Defining a Clinically Relevant Thyroglobulin Antibody Interference Threshold for High-Sensitivity Thyroglobulin Immunoassays

Strategic Insights -

Research conducted at the University of Pittsburgh Medical Center has shed light on the interpretation of serum thyroglobulin (Tg) levels in differentiated thyroid cancer. The study found that thyroglobulin antibodies (TgAb) can interfere with Tg measurements, making it challenging to determine a standardized threshold for interference. The researchers implemented a new instrument and observed an increase in TgAb-positive samples, which reflexed to alternate send-out Tg methods with reduced analytic sensitivity but were more robust to TgAb interference.

Key Takeaways:

  • The study analyzed 119 serum specimens with an electrochemiluminescent TgAb immunoassay (ECLIA-TgAb) and compared TgAb measurements by radioimmunoassay (RIA-TgAb) and Tg levels measured via immunometric assay (IMA-Tg) and RIA (RIA-Tg; reference method).
  • Increasing the ECLIA-TgAb threshold to 20 IU/mL improved concordance to 90% between IMA-Tg and RIA-Tg, and qualitative agreement between IMA-Tg and RIA-Tg increased to 95%.
  • Retrospective chart review indicated that implementing a 20 IU/mL threshold would result in no change in patient management, reducing send-out testing by 66%.
  • The researchers suggested that defining a clinically relevant TgAb interference threshold for high-sensitivity Tg immunoassays offers an accessible and practical strategy for individual laboratories to maximize the samples eligible for highly sensitive Tg measurement.

Statistics:

  • 30% of ECLIA-TgAb specimens above the LOD (10 IU/mL) were positive by RIA-TgAb.
  • Increasing the ECLIA-TgAb threshold to 20 IU/mL improves concordance to 90% between IMA-Tg and RIA-Tg.
  • Implementing a 20 IU/mL threshold would reduce send-out testing by 66%.
  • 95% of Tg levels measured via IMA-Tg agreed with RIA-Tg levels when the ECLIA-TgAb threshold was set at 20 IU/mL.

Sources:

  • Defining a clinically relevant thyroglobulin antibody interference threshold for high-sensitivity thyroglobulin immunoassays: a single institution case study. Clinical Biochemistry, 2025:110995.
  • Clinical Biochemistry can be contacted at: Pergamon-elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, England.