Serum Tg--a sensitive marker of thyroid abnormalities and iodine deficiency in epidemiological studies.

Serum Tg is widely used in the control of thyroid cancer but also in the diagnosis of certain other thyroid diseases. Serum Tg may be useful in the characterization of the iodine status of a population, but little is known about determinants of serum Tg levels. We examined a random selection of 4,649 subjects from 2 regions in Denmark with different iodine status. Thyroid volume and structure were determined with ultrasonography, and thyroid function tests and Tg analysis were performed. The factor with the closest association with serum Tg levels was thyroid volume at ultrasonography (P < 0.001). Also thyroid nodularity (P < 0.001) and iodine excretion (P < 0.001) had close associations to serum Tg, even after adjusting for the influence of the other parameters. Thyroid dysfunction had a less pronounced but still highly significant association with serum Tg (P < 0.001), but no relation was found to serum TSH in general. The association with age seemed to rely on differences in the prevalence of thyroid abnormalities, and men had lower Tg levels than women of the same age. There was a marked difference in serum Tg between the two regions with slightly different iodine excretion also after adjusting for the other factors. In conclusion, serum Tg reflects thyroid abnormalities and thyroid function and is a sensitive marker of iodine deficiency in a population.