Thyroglobulin

What it isThyroglobulin is the storage protein within the thyroid follicle where T4 and T3 are made. Small amounts leak into circulation.

DoesActs as a tumor marker after thyroid cancer treatment — detectable thyroglobulin after total thyroidectomy and radioiodine ablation suggests residual or recurrent disease.

GoodUndetectable in post-treatment thyroid cancer patients signals successful eradication.

BadDetectable thyroglobulin in those settings flags recurrence; also rises in benign thyroid conditions.