Why do my levels of thyroglobulin (Tg) fluctuate?
There are several possibilities, including the presence or absence of antibodies against thyroglobulin, and the use of different assays to measure thyroglobulin, as outlined in Discordant serum thyroglobulin results generated by two classes of assay in patients with thyroid carcinoma: correlation with clinical outcome after 3 years of follow-up. Cancer. 2003 Jul 1;98(1):41-7. Indeed, the newer more sensitive thyroglobulin assays which do not use radioactive tracers are more widely used, but are more prone to interference from circulating antithyroglobulin antibodies which can greatly compromise the accuracy of the thyroglobulin test. Hence, measurement of thyroid antibodies should always be done at the same time the thyroglobulin is measured. Some experts have advocated that the use of the newer highly sensitive Tg assays may one day supplant the need for a TSH-stimulated thyroglobulin in many patients. For an excellent overview of this area, see Measuring thyroglobulin and thyroglobul
