Anti-Thyroglobulin Antibody Test
The anti-thyroglobulin (anti-Tg) antibody test measures antibodies against thyroglobulin — a protein produced by thyroid cells.
It serves two purposes: detecting autoimmune thyroid disease and monitoring thyroid cancer after treatment.
Last medically reviewed: 1 November 2025
As an autoimmune marker
Anti-Tg antibodies appear in autoimmune thyroiditis alongside anti-TPO. They are less sensitive than anti-TPO for diagnosing Hashimoto’s but support the diagnosis when positive.
They are less commonly ordered alone — usually checked with anti-TPO for a complete autoimmune picture.
As a cancer marker
After total thyroidectomy for differentiated thyroid cancer, thyroglobulin becomes a tumour marker — rising levels suggest recurrence. However, anti-Tg antibodies interfere with thyroglobulin assays, so anti-Tg levels are monitored alongside.
Persistently rising anti-Tg after cancer treatment may indicate autoimmune activity or residual disease — interpretation requires specialist context.
Interpretation
Positive anti-Tg supports autoimmune thyroiditis when thyroid dysfunction is present. In cancer follow-up, trends matter more than absolute values — rising levels warrant investigation.
Results must be interpreted with thyroid function tests and clinical context.
Frequently asked questions
Why is anti-Tg checked after thyroid cancer?
Anti-Tg antibodies interfere with thyroglobulin measurement — the key tumour marker after thyroidectomy. Monitoring both ensures accurate surveillance.
Is anti-Tg as important as anti-TPO?
For diagnosing Hashimoto’s, anti-TPO is more sensitive. Anti-Tg is complementary and particularly important in cancer follow-up.
Can anti-Tg be positive without thyroid disease?
Rarely — low-level positivity can occur, but significant titres usually indicate autoimmune thyroiditis or post-surgical changes.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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