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Defining a clinically relevant thyroglobulin antibody interference threshold for high-sensitivity thyroglobulin
Simmi Patel1, Octavia M Peck Palmer2, Chanda B Lay1
1Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
Clinical Biochemistry
|August 23, 2025
Summary
A new 20 IU/mL threshold for thyroglobulin antibody (TgAb) testing improves monitoring of differentiated thyroid cancer patients. This change reduces costly send-out tests while ensuring accurate thyroglobulin (Tg) level interpretation.
Area of Science:
- Clinical Chemistry
- Endocrinology
- Thyroid Cancer Diagnostics
Background:
- Thyroglobulin (Tg) level interpretation in differentiated thyroid cancer is often confounded by thyroglobulin antibodies (TgAb).
- Current methods lack standardized thresholds for TgAb interference, leading to issues with sensitive Tg monitoring.
- Implementation of new assays resulted in increased TgAb-positive samples, necessitating less sensitive methods, increasing costs, and delaying results.
Purpose of the Study:
- To evaluate the impact of a new thyroglobulin antibody (TgAb) assay threshold on the monitoring of differentiated thyroid cancer (DTC).
- To determine if a higher TgAb threshold could improve the utility of sensitive thyroglobulin (Tg) immunoassays.
- To assess the clinical relevance of TgAb interference and establish an optimal threshold for Tg testing.
Main Methods:
- Analyzed 119 serum specimens using an electrochemiluminescent TgAb immunoassay (ECLIA-TgAb) with an initial threshold of 10 IU/mL.
- Compared TgAb measurements with radioimmunoassay (RIA-TgAb) and Tg levels measured by immunometric assay (IMA-Tg) and RIA (RIA-Tg).
- Assessed clinical concordance and patient management with a revised ECLIA-TgAb threshold of 20 IU/mL.
Main Results:
- Increasing the ECLIA-TgAb threshold from 10 IU/mL to 20 IU/mL improved concordance with RIA-TgAb to 90%.
- A 20 IU/mL threshold optimized qualitative agreement between sensitive IMA-Tg and reference RIA-Tg assays (95%).
- Retrospective chart review confirmed no change in patient management decisions with the revised threshold.
Conclusions:
- An ECLIA-TgAb threshold of 20 IU/mL enables more patients to be monitored using the sensitive IMA-Tg method.
- This revised threshold significantly reduces the need for costly, less sensitive send-out Tg testing (by 66%).
- This strategy provides a practical approach for laboratories to optimize TgAb thresholds for accurate and efficient DTC monitoring.
