Thyroglobulin: a clinical review

The introduction of the new assays for thyroglobulin (Tg) with a sensitivity of 1 to 3 mg/L has made it unnecessary to terminate thyroxine suppression therapy to determine Tg level. Thyroid-stimulating hormone should always be assessed in conjunction with the Tg to ensure that it is not high; as long as it is suppressed to normal, subnormal suppression is unnecessary. A total thyroidectomy is not a prerequisite for using Tg as a tumor marker; the Tg is equally reliable in those patients who have undergone a near-total or a subtotal thyroidectomy. Even patients who have undergone only a lobectomy may benefit from Tg monitoring if the level is low; however, an initial high Tg level (without a previous low Tg value) should not be interpreted as suggestive of cancer. Postoperative 131 I ablation is not necessary for an accurate Tg measurement. The finding of anti-Tg antibodies in patients with thyroid cancer remains a major problem, but other technical problems related to the absence of an international Tg standard have now been eliminated. Monitoring the Tg level reliably detects early recurrent disease in patients who have undergone a surgical procedure for thyroid carcinoma and are receiving thyroxine suppression therapy. Only those patients with Tg levels that exceed 3 to 5 mg/L or with clinical evidence of recurrence need to discontinue thyroxine treatment and have a 131 I scan. This approach can substantially decrease the expense, inconvenience, and morbidity of performing routine scans on these patients.