What does the Thyroglobulin Antibody (Anti-TG) test measure?

Why is Thyroglobulin Antibody (Anti-TG) measured?

Anti-TG serves two distinct clinical roles within the comprehensive thyroid panel. As an autoimmune thyroid disease marker, Anti-TG is present in approximately 60–80% of Hashimoto's thyroiditis cases and 50–70% of Graves' disease cases — and is diagnostically essential in the minority of patients (approximately 5–10%) who are Anti-TPO-negative but Anti-TG-positive, where Anti-TPO alone would miss the autoimmune diagnosis. As a thyroid cancer monitoring marker, Anti-TG positivity is a critical interpretive confounder in differentiated thyroid cancer (papillary and follicular) surveillance — Anti-TG antibodies interfere with serum thyroglobulin immunoassays, causing falsely low thyroglobulin measurements that underestimate tumour recurrence or residual disease. In thyroid cancer follow-up, Anti-TG positivity must always be documented alongside thyroglobulin levels.

Reference ranges

Standard reference

<115 IU/mL (negative) # REVIEWER FLAG: Confirm Access Medical Laboratories reference range for Anti-TG — positivity thresholds vary between immunoassay platforms. Some laboratories use <20 IU/mL; others <115 IU/mL depending on assay calibration. Confirm Access Medical Laboratories' specific cut-off.

Functional medicine optimal

Not applicable — Anti-TG is a qualitative autoimmunity marker; negative is the target. As with Anti-TPO, serial titre monitoring has limited actionable clinical utility in the autoimmune thyroid disease context.

Units

IU/mL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.