Thyroglobulin (Tg) is a very abundant protein found only in thyroid tissue. Even a trace of thyroglobulin in the blood indicates that normal or abnormal thyroid tissue is present. Measuring thyroglobulin levels is mainly useful in monitoring differentiated thyroid cancer to ensure that all thyroid tissue has been removed by surgery and radioactive iodine therapy.
After thyroid ablation, thyroglobulin levels sometimes require the residual thyroid tissue to be “awakened” by increasing endogenous TSH secretion by the pituitary gland (suspension of thyroid hormone therapy), or by directly injecting biosynthetic TSH (Thyrogen©). Since low levels of thyroglobulin may indicate a recurrence of cancer, it is necessary to ensure that the anti-thyroglobulin antibodies often present in individuals do not interfere with the thyroglobulin test (see that section). To prevent variances caused by the use of different testing techniques, thyroid cancer should always be monitored using the same testing technique.
Apart from specific thyroid cancer monitoring, the measurement of thyroglobulin levels is of little clinical utility compared to regular thyroid function tests (TSH, T4 and T3).