Thyroglobulin (Tg) is a large protein produced exclusively by thyroid follicular cells and serves as the precursor from which thyroid hormones T4 and T3 are synthesised. In healthy individuals, small amounts of thyroglobulin leak into the bloodstream. After total thyroidectomy or radioiodine ablation for thyroid cancer, thyroglobulin levels should fall to undetectable or very low levels.
Rising thyroglobulin after treatment is an early and sensitive indicator of thyroid cancer recurrence — often detectable before any imaging changes appear. Thyroglobulin must always be interpreted alongside thyroglobulin antibodies (TgAb), which interfere with the assay and can cause falsely low readings if present.
FAQs
Why must thyroglobulin and TgAb always be measured together?
TgAb causes falsely low thyroglobulin results. A patient could appear disease-free due to TgAb interference rather than true remission. Both must be measured simultaneously for accurate interpretation.
What is TSH-stimulated thyroglobulin?
Stopping levothyroxine or giving recombinant TSH (Thyrogen) raises TSH, stimulating residual thyroid tissue to produce thyroglobulin. Stimulated thyroglobulin is more sensitive for detecting small recurrences than suppressed thyroglobulin.
Can thyroglobulin detect cancer before imaging?
Yes. Rising thyroglobulin often indicates biochemical recurrence before lesions are visible on imaging. Whole body scintigraphy or FDG PET-CT can locate the source.
Is thyroglobulin useful with an intact thyroid?
Only in limited contexts. With an intact thyroid, thyroglobulin reflects total thyroid tissue mass, not cancer specifically. It is most meaningful as a cancer marker after complete thyroidectomy and ablation.
