Iervasi A et al. (2007) Clinical relevance of highly sensitive Tg assay in monitoring patients treated for differentiated thyroid cancer. Clin Endocrinol 67: 434–441

Serum thyroglobulin is a highly specific marker for residual thyroid tissue and/or recurrence or metastases in patients previously treated for differentiated thyroid cancer (DTC).

Iervasi et al. analyzed the effects of using a highly sensitive automated thyroglobulin assay in 160 consecutive patients treated for DTC (mean age 51.2 years). Results were compared with those obtained using a routinely employed assay. Thyroglobulin was measured during suppression of endogenous TSH by levothyroxine and after stimulation with recombinant human TSH (rhTSH).

The measurable amount of thyroglobulin is 0.9 µg/l with the standard assay and 0.1 µg/l with the highly sensitive assay. The response to rhTSH was classified as 'positive' if thyroglobulin levels were >2 µg/l or as 'negative' if they remained <2 µg/l.

With the standard assay, thyroglobulin was undetectable during suppression with levothyroxine in all patients who later had a 'negative' response to rhTSH. Thyroglobulin was detectable in 17% of patients who later had a 'positive' response to rhTSH.

With the highly sensitive assay, thyroglobulin was undetectable during suppression with levothyroxine in 90% of patients who later had a 'negative' response to rhTSH. Thyroglobulin was detectable in all patients who later had a 'positive' response to rhTSH.

The authors conclude that assays with a higher functional sensitivity could be a useful diagnostic tool in the follow-up of patients treated for DTC, allowing for the detection of thyroglobulin concentrations not otherwise measurable and for earlier identification of persistent or recurrent disease.